Apparatus for assembling a reticle assembly - Patent application

Abstract

To provide an object handling apparatus for handling a generally planar object.SOLUTION: An object handling apparatus comprises two support arms. At least one of the two support arms is movable relative to the other support arm generally in a plane such that the two support arms are operable to grip and hold an object disposed in the plane. Each of the support arms includes at least one support pad and at least one aligner. The support pads are configured to locally contact a surface of the object and apply a force thereto generally perpendicular to the plane so as to support the object. The aligners are configured to locally contact a surface of the object and apply a force thereto generally in the plane so as to align the object.SELECTED DRAWING: Figure 22B

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to EP Application No. 19159943.0, filed February 28, 2019, EP Application No. 19163828.7, filed March 19, 2019, and EP Application No. 19191214.6, filed August 12, 2019, each of which is incorporated herein by reference in its entirety.

[0002]

[0002] The present invention relates to an apparatus and associated method for the assembly of a reticle assembly for a lithographic apparatus, the reticle assembly comprising a pellicle assembly connected to a reticle. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on that substrate. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength within 4-20 nm, can be used to form smaller features on a substrate than conventional lithographic apparatus (which can use electromagnetic radiation with a wavelength of 193 nm, for example).

[0005]

[0005] A patterning device (e.g. a mask) used to impart a pattern to a radiation beam in a lithographic apparatus may form part of a mask assembly. The mask assembly may include a pellicle that protects the patterning device from particle contamination. The pellicle may be supported by a pellicle frame.

[0006] It would be desirable to provide an apparatus that obviates or mitigates one or more problems associated with the prior art. Summary of the Invention

[0007] According to a first aspect of the present invention, there is provided an object handling apparatus for handling generally planar objects, the object handling apparatus comprising two support arms, at least one of which is movable generally in-plane relative to the other support arm such that the two support arms are operable to grasp and hold an object disposed in-plane, each of the support arms including at least one support pad and at least one alignment portion, the support pad configured to locally contact a surface of the object and apply a force to the surface generally perpendicular to the surface to support the object, and the alignment portion configured to locally contact the surface of the object and apply a force generally in-plane to the surface to align the object.

[0008]

[0008] The object handling apparatus is advantageous because it reduces the amount of friction between the arm and the object. This in turn can reduce the amount of particle debris that can be generated by such friction. The object can be a pellicle assembly or a patterning device. Because it is particularly important that the pellicle assembly or patterning device remain clean and free of contaminants, the object handling apparatus is particularly advantageous for use when handling these objects.

[0009] It will be appreciated that each of the support pads and alignment features only locally contacts the object, and therefore only a relatively small portion of the object. Advantageously, this may reduce the risk of generating particle contaminants (compared to support features that contact the entire periphery of the pellicle assembly or patterning device).

[0010]

[0010] The alignment section is positioned to ensure that when an object is grasped by the support arm, the object is in a known fixed position relative to the object handling device.

[0011] According to a second aspect of the present invention, there is provided an object handling apparatus for handling generally planar objects, the object handling apparatus comprising: two support arms, at least one of which is movable generally in a plane relative to the other support arm such that the two support arms are operable to grip and hold an object disposed in the plane; a support structure; and a damper assembly, the two support arms connected to the support structure via the damper assembly, the damper assembly being configured to damp movement of the object in a direction perpendicular to the plane of the object when the object is gripped by the support arms.

[0012] The object can be either a pellicle assembly or a patterning device, and the damper assembly can be configured to damp movement of the object (e.g., the pellicle assembly or the patterning device) in a direction in which the object is generally presented to the object handling apparatus.

[0013] The support structure may be a rail. Advantageously, such a mechanism may move the position of the pellicle assembly or patterning device along the track of the rail while preventing damage to the pellicle assembly or patterning device (e.g., caused by dropping the pellicle assembly or patterning device).

[0014] According to a third aspect of the present invention, there is provided a pellicle frame mounting apparatus comprising: a pellicle assembly handling apparatus configured to handle a pellicle assembly; a patterning device handling apparatus configured to handle a patterning device; and rails, the pellicle assembly handling apparatus comprising a support arm configured to grip and hold the pellicle assembly; the patterning device handling apparatus comprising a support arm configured to grip and hold the patterning device; the pellicle assembly handling apparatus supported by and movable relative to one of the rails; and the patterning device handling apparatus supported by and movable relative to one of the rails.

[0015]

[0015] In a lithographic apparatus, a mask assembly may be used. The mask assembly may comprise a patterning device (which imparts a desired pattern to a radiation beam during use) and a pellicle assembly (which prevents contaminant particles from reaching the patterning device). The pellicle assembly may include an engagement mechanism affixed to a frame of the pellicle assembly. The pellicle assembly may be attached to the patterning device via the engagement mechanism using a stud. The pellicle assembly may be attached to the patterning device using a pellicle frame mounting arrangement.

[0016] When securing the pellicle assembly to the patterning device (thereby forming a mask assembly), it is important that the engagement features of the pellicle assembly and the studs of the patterning device are handled carefully and well aligned. The pellicle frame mounting apparatus may include pellicle assembly handling apparatus and patterning device handling apparatus for accurately and carefully grasping, moving, and positioning the pellicle assembly and patterning device.

[0017]

[0017] The pellicle assembly handling apparatus may include a portion that can be described as a pellicle assembly gripper. The patterning device handling apparatus may include a portion that can be described as a patterning device gripper. The gripper may be movably mounted on a rail. The gripper may be operable to be manually moved along a track disposed within the rail. Advantageously, movably mounting the pellicle assembly gripper and the patterning device gripper on a common rail allows for accurate and safe handling of the pellicle assembly and the patterning device.

[0018] A pellicle assembly handling apparatus may include an object handling apparatus according to the first aspect of the invention.

[0019] The patterning device handling apparatus may include an object handling apparatus according to the first aspect of the invention.

[0020] The pellicle assembly handling apparatus may include an object handling apparatus according to the second aspect of the invention.

[0021] A patterning device assembly handling apparatus may include an object handling apparatus according to the second aspect of the invention.

[0022] According to a fourth aspect of the present invention, there is provided a measurement system for measuring an object, the measurement system comprising a radiation source for generating a beam of unpolarized radiation, a beam splitter, a quarter wave plate and an imaging sensor, the radiation source arranged such that a portion of the unpolarized radiation propagates through the beam splitter and the quarter wave plate, and the imaging sensor arranged such that a reflected portion of the portion of the unpolarized radiation is incident on the imaging sensor after passing through the quarter wave plate and the beam splitter.

[0023]

[0023] The optical measurement system may be operable to measure the position of the pellicle frame. The optical measurement system may include a radiation source, a beam splitter, a quarter wave plate, and an imaging sensor.

[0024]

[0024] The radiation source may emit unpolarized light. The unpolarized light may be split by a beam splitter, which may result in linearly polarized light. At least a portion of the linearly polarized light may then propagate through a quarter-wave plate and become circularly polarized. The pellicle assembly (including the pellicle and pellicle frame) and patterning device (such as a reticle) may be positioned such that the circularly polarized light propagates through the pellicle and / or pellicle frame before being reflected from the patterning device. The reflected circularly polarized light may then propagate through the quarter-wave plate and beam splitter and be incident on an imaging sensor. Measurements made by the imaging sensor allow the position of the pellicle frame (and therefore the pellicle assembly) to be determined.

[0025] At least a portion of the circularly polarized beam generated by the quarter-wave plate may be incident on the patterning device and reflected by the patterning device. The edge of the pellicle frame may block the light reflected from the patterning device. At least a portion of the radiation reflected from the patterning device may be incident on the imaging sensor, where it may have a measured spatial intensity (e.g., a measured image) that varies depending on the position of the edge of the pellicle frame. In particular, differences in the light transmission levels between the pellicle and the pellicle frame may provide spatial contrast in the intensity measurement. This spatial contrast may be particularly useful in measuring the position of the pellicle assembly and subsequently in aligning the pellicle assembly.

[0026]

[0026] The quarter-wave plate performs a phase shift (between two orthogonal components of the electric field intensity) on the light reflected from the patterning device MA as it propagates through the quarter-wave plate. This phase shift is performed so that the light reflected from the patterning device MA is maximally transmitted through the beam splitter. Maximum transmission of light through the beam splitter results in a high signal in the intensity measurement performed by the imaging sensor. For example, measurements performed by the imaging sensor are subject to background light, which can reduce the contrast of the image representing the edges of the pellicle and pellicle frame. However, because such background radiation is unpolarized, only a portion (e.g., half) of such background radiation may reach the imaging sensor. In contrast, the signal radiation (i.e., the portion of the radiation reflected from the patterning device) is maximally transmitted through the beam splitter. Advantageously, maximal transmission of this signal light through the beam splitter results in high spatial contrast in the measurement performed by the imaging sensor. This allows the position of the pellicle assembly to be measured with high precision.

[0027] According to a fifth aspect of the present invention, there is provided a measurement system for measuring the position of an object relative to a reference object, the object being provided with an object marker and the reference object being provided with a window comprising the reference marker, the measurement system comprising a radiation source for generating a radiation beam, and an imaging sensor, the radiation source being arranged such that the radiation beam is incident on the reference marker and the object marker at an angle such that reflected diffraction orders of the radiation are normally incident on the imaging sensor.

[0028]

[0028] The optical measurement system may be operable to measure the position of the object relative to a reference object. The object may be a patterning device (such as a reticle). The object may be provided with an object marker. The object marker may comprise a diffraction grating. The object marker may comprise an alignment mark. The reference object may be a window. The reference object may be provided with a reference marker. The reference marker may comprise a diffraction grating. The reference marker may comprise an alignment mark. The optical measurement system may include a radiation source and an imaging sensor.

[0029]

[0029] The radiation source may emit a light beam. The beam may propagate toward the object and the reference object. A portion of the beam may be backscattered (e.g., reflected) from the reference marker. Another portion of the beam may be transmitted through the reference object. This portion of the beam may then be backscattered (e.g., reflected) from the object marker. Each of the object marker and the reference marker may be arranged to form a reflective diffraction grating. The portion of the beam backscattered from each of the object marker and the reference marker may form multiple diffraction orders. The first-order reflected beam may be incident on the imaging sensor. The imaging sensor may therefore be operable to measure a signal corresponding to the position of the object relative to the reference object. The zero-order reflected beam (corresponding to the standard reflection) may not be incident on the imaging sensor. The optical measurement system may be operable to measure the positions of the object marker (fixed relative to the object) and the reference marker (fixed relative to the reference object). The optical measurement system may therefore be operable to measure the position of the object relative to the reference object. This may be used to align the object with the reference object. For example, an optical measurement system can be used to align a patterning device with another apparatus.

[0030] Advantageously, by measuring the diffraction orders of light (as described above) and measuring the positions of the object marker and the reference marker using the same measurement apparatus (optical measurement system), an accurate measurement of the position of the object relative to the reference object can be obtained, which may result in a more accurate measurement of the object position (such as a patterning device) than would be possible if the position of the object (such as a patterning device) were based on measuring the position of an edge of the object (such as an edge of the patterning device).

[0031]

[0031] A pellicle frame mounting device including the measurement system according to the fourth aspect of the present invention or the measurement system according to the fifth aspect of the present invention.

[0032] According to a sixth aspect of the present invention, there is provided a pellicle frame mounting device comprising: a support structure configured to support a pellicle assembly; and a linearly movable actuation pin configured to move relative to the support structure when supported by the support structure so as to contact a distal end of an engagement arm of an engagement mechanism affixed to the frame of the pellicle assembly and elastically bend the engagement arm, the actuation pin extending in a direction generally perpendicular to the engagement arm and movable in this direction, and a surface of the actuation pin having a convex curved surface that minimizes the contact surface area between the surface and the engagement arm.

[0033]

[0033] When the actuation pin moves and contacts a generally vertical engagement arm (e.g., a resilient cantilever engagement arm), it moves the distal end of the engagement arm, thereby rotating the engagement arm. When the actuation pin moves in a linear direction, the contact point between the actuation pin and the engagement arm moves along the surface of the engagement arm. By providing a convex curved surface on the actuation pin, the contact surface area between the actuation pin and the engagement arm is minimized. This configuration ensures that slippage between the actuation pin and the engagement arm is minimized. Advantageously, this can reduce the risk of particle contamination (compared to components sliding against each other at the interface between the actuation pin and the engagement arm).

[0034]

[0034] The apparatus further comprises an actuator operable to move the position of the support structure, and a plurality of hooked pins disposed on and protruding from the support table, the plurality of hooked pins configured to releasably clamp the engagement mechanism in a predetermined position relative to the support structure during engagement or disengagement of the pellicle assembly and the patterning device, and either or both of the actuator or the plurality of removable inserts on which the hooked pins are provided can be removed from the support table if movement of the support table is obstructed.

[0035] The hooked pins can be useful for keeping the pellicle assembly fixed to the support structure during engagement or disengagement of the pellicle assembly from the patterning device. This allows movement of the support structure to cause corresponding movement of the pellicle assembly. However, there are cases where the hooked pins cannot be disengaged from the pellicle frame. The above-described detachment mechanism provides a safety mechanism to detach the hooked pins from the actuation mechanism if movement is obstructed, preventing damage to the pellicle assembly. In some embodiments, the detachment mechanism can allow the support table to be detached from the actuator. In some embodiments, the detachment mechanism can be achieved by providing the hooked pins on a removable insert (which is removably connected to the support structure).

[0036] According to a seventh aspect of the present invention, there is provided a stud attachment apparatus comprising a support structure configured to hold a patterning device and a stud operating portion configured to bring a stud into contact with the patterning device, the stud operating portion being attached to the outer frame using a plurality of leaf springs.

[0037]

[0037] To enable attachment of the pellicle assembly to the patterning device, studs may be attached to the patterning device. The studs may be attached to the patterning device using a stud attachment apparatus. The stud attachment apparatus may include a stud handling portion for handling the stud. The stud handling portion may be attached to the outer frame. The attachment may include a plurality of leaf springs. The plurality of leaf springs allow some relative movement between the stud handling portion and the outer frame (e.g. when the base of the stud contacts the patterning device).

[0038]

[0038] Each leaf spring is dimensioned to allow movement of the stud operating portion (relative to the outer frame) in a direction that allows the stud to be attached to the patterning device (e.g. the z direction), but negligible movement in other directions. Furthermore, by using multiple leaf springs rather than a single leaf spring, rotation of the stud operating portion (and consequently the stud) in the xz or yz planes is negligible. Advantageously, this allows for more controlled positioning of the stud, allowing for more accurate placement of the stud on the patterning device.

[0039]

[0039] The stud operating portion may include a stud holder arranged to hold the stud under gravity or using a vacuum mechanism.

[0040] The stud handling unit may include a glue dispenser. The glue dispenser may be configured to dispense a poly(methyl methacrylate)-based glue. As used herein, poly(methyl methacrylate)-based glue may be referred to as PMMA glue. The glue dispenser may be configured to provide the PMMA glue in one or more components. The glue dispenser may be configured to provide at least one component of the PMMA glue to a surface of a stud. The glue dispenser may be configured to provide at least one component of the PMMA glue to a surface of a patterning device. The glue dispenser may be configured to provide at least one component of the PMMA glue to a surface of a stud and at least one component of the PMMA glue to a surface of a patterning device. When the stud handling unit contacts the stud with the patterning device, the stud can be affixed to the patterning device with the PMMA glue.

[0041]

[0041] PMMA glue comprises a thermoplastic resin formed by polymerization of methyl methacrylate (MMA) monomer. PMMA glue is generally a resin formulation containing MMA monomer and one or more other components, such as initiators, accelerators, crosslinkers, and other additives. As used herein, it will be appreciated that providing a PMMA glue to a surface refers to providing one or more components of the PMMA glue (e.g., the accelerator- or initiator-containing resin component of the PMMA glue) to that surface. Furthermore, as used herein, it will be appreciated that contacting a surface with another surface refers to indirectly contacting two surfaces with each other (e.g., via a glue adhering to both surfaces).

[0042] For example, the PMMA glue process involves providing a first glue component containing a mixture of MMA monomer and an accelerator, and a second glue component containing a mixture of MMA monomer and an initiator. Preferably, the initiator is provided in an amount appropriate for the total amount of the first and second glue components when combined. The glue components can be applied, for example, by applying the first glue component to a first substrate and the second glue component to a second substrate. For example, the first glue component containing MMA monomer can be applied to the surface of a pellicle frame, and the second glue component containing an initiator can be applied to the surface of a patterning device that will be bonded to the pellicle frame coated with the first glue component. Alternatively, the two glue components can be applied in reverse. Once the two substrates are bonded, curing occurs.

[0043]

[0043] PMMA glue can be used to bond a surface of the first lithography component to a surface of the second lithography component. At least one of the first and second lithography components can be a component of an EUV lithography apparatus. For example, the first lithography component is a pellicle and the second lithography component is a pellicle frame. In another example, the first lithography component is a pellicle frame and the second lithography component is a patterning device. In yet another example, the first lithography component is a first pellicle frame component, such as a first component of a pellicle frame engagement mechanism, and the second lithography component is a second component of the pellicle frame engagement mechanism.

[0044] In an alternative method, the first and second components can be provided side by side on a single substrate, and then a second substrate can be provided on top of that, sandwiching the PMMA glue component between the two substrates. In this alternative method, curing occurs when the first and second components are brought into proper contact with each other by being trapped between the two surfaces. Other alternative processing methods may also be applied.

[0045] The PMMA glue component can be applied as a single continuous shape, such as a layer, or as discrete beads. The advantage of applying the adhesive as a bead is that it reduces tension in the surfaces being glued, such as between a pellicle and a frame, or between a frame and a reticle surface. In such cases, the bead acts as a resilient spring between the two surfaces.

[0046] Preferably, the thickness of the layer or bead is less than 0.6 mm, more preferably less than 0.5 mm, to allow for optimal polymerization, which begins on one side of the layer or bead and progresses to the other side.

[0047]

[0047] In this specification, a bead refers to a discrete portion of the glue component rather than a continuous layer, and may have any shape such as spherical, hemispherical, or quasi-rectangular, depending on the wettability and viscosity of the PMMA resin.

[0048]

[0048] The viscosity of the PMMA resin is preferably at least 8000 mPas, more preferably at least 10,000 mPas. The curing of the PMMA glue can be accelerated chemically or by the application of heat.

[0049] The glue or adhesive used to attach the pellicle membrane to the pellicle frame or the pellicle frame to the reticle preferably has a lap shear strength of >5 MPa, preferably >10 MPa, when tested according to standard ISO 4587 (OI3). The Young's modulus of the glue or adhesive used to attach the pellicle membrane to the pellicle frame or the pellicle frame to the reticle is preferably in the range of 0.5 to 10 GPa, more preferably 1 to 5 GPa, when measured according to ISO 527.

[0050]

[0050] Preferably, the outgassing of the glue or adhesive used to attach the pellicle membrane to the pellicle frame or the pellicle frame to the reticle is <6E-06 [mbar.l / s.cm2], more preferably <8E-09 [mbar.l / s.cm2], more preferably <8E-10 [mbar.l / s.cm2].

[0051] According to an eighth aspect of the present invention, there is provided a pellicle mounting apparatus. The pellicle mounting apparatus includes a pellicle manipulation unit and a glue dispenser. The pellicle mounting apparatus can be for fabricating at least a portion of a pellicle assembly from a first item and a second item. The pellicle manipulation unit can be configured to contact the first item with the second item. The glue dispenser can be configured to provide PMMA glue in one or more components. The glue dispenser can be configured to provide at least one component of the PMMA glue to a surface of the first item. The glue dispenser can be configured to provide at least one component of the PMMA glue to a surface of the second item. The glue dispenser can be configured to provide at least one component of the PMMA glue to a surface of the first item and at least one component of the PMMA glue to a surface of the second item. When the first article is brought into contact with the second article, the first article can be attached to the second article by the PMMA glue.

[0052] The first article is a frame, and the frame can be a pellicle frame. The second article can be a pellicle (i.e., a thin film or membrane). The pellicle frame can be a frame constructed to provide an enclosed space when the pellicle frame is bonded to a patterning device.

[0053] The second item can be an engagement mechanism.

[0054]

[0054] The pellicle handling portion may include means for applying tension to the pellicle. For example, the pellicle handling portion may apply tension to the pellicle before contacting the pellicle with the frame.

[0055] According to a ninth aspect of the present invention, there is provided a pellicle assembly. The pellicle assembly may include a pellicle. The pellicle assembly may include a frame. PMMA glue may be disposed between and in contact with the pellicle and the frame to adhere the pellicle to the frame.

[0056] According to a tenth aspect of the present invention, there is provided a patterning device. The patterning device may include a plurality of studs. PMMA glue may be disposed between and in contact with each stud of the plurality of studs so as to attach the patterning device to each stud of the plurality of studs.

[0057] According to an eleventh aspect of the present invention, there is provided a mask assembly comprising a pellicle assembly according to the ninth aspect of the present invention and a patterning device according to the tenth aspect of the present invention.

[0058]

[0058] The use of PMMA glue offers several advantages.

[0059] The curing process of the PMMA glue takes several minutes to complete, which is a significantly shorter curing process than the curing process of known epoxy glues, which typically takes several hours. Therefore, using PMMA glue to attach a pellicle frame to a pellicle in accordance with some aspects of the present invention advantageously significantly reduces the time required to produce a pellicle assembly (compared to using known epoxy glues). Furthermore, using PMMA glue to attach studs to a patterning device advantageously significantly reduces the time required (compared to using known epoxy glues). Relatedly, this provides advantages for mass production.

[0060]

[0060] Generally, PMMA glues are more elastic than epoxy glues. PMMA glues can be more easily removed from a surface (e.g., from the surface of a patterning device) than epoxy glues. Advantageously, therefore, using PMMA glue to attach studs to a patterning device facilitates the stud removal procedure (compared to using known epoxy glues) and the procedure for cleaning the patterning device after the studs have been removed.

[0061]

[0061] In order to accelerate the curing of known epoxy glues, it may be necessary to heat the known epoxy glues using a heater and / or oven. Advantageously, no heating is required to accelerate the curing of PMMA glues. As a result, the manufacturing procedure is further simplified and the risk of defects and damage to the manufactured product (pellicle assembly or patterning device provided with studs) can also be reduced.

[0062] According to a twelfth aspect of the present invention, there is provided a mask assembly. The mask assembly may include a pellicle assembly and a patterning device. The pellicle assembly may include a pellicle and a frame. An adhesive may be disposed between and in contact with the frame and the patterning device so as to affix the frame to the patterning device.

[0063]

[0063] The adhesive may be provided in a single continuous shape, which may generally conform to the shape of the frame.

[0064]

[0064] A sealed space may be formed between the pellicle assembly and the patterning device, in such an embodiment the pellicle assembly is referred to as a "closed frame" system.

[0065]

[0065] The adhesive may be PMMA glue.

[0066] A mask assembly according to the twelfth aspect of the present invention is advantageous for several reasons.

[0067] A mask assembly according to the twelfth aspect of the present invention may provide a sealed space between the pellicle assembly and the patterning device, which may advantageously prevent contaminant particles from entering the space and causing errors in the pattern applied to the substrate by the lithographic apparatus.

[0068]

[0068] As will now be discussed, the mask assembly according to the twelfth aspect of the present invention is particularly advantageous compared to known mechanisms which typically use intermediate fixing members (known as studs) that are affixed to the patterning device and engage with the pellicle assembly.

[0069]

[0069] The mask assembly according to the twelfth aspect of the present invention includes fewer components than a mask assembly that uses intermediate fixing members such as studs (attached to the patterning device) and engagement mechanisms (provided on the pellicle assembly) that engage with the intermediate fixing members (studs). Advantageously, therefore, the mask assembly according to the twelfth aspect of the present invention may be relatively simple to manufacture. The fewer components and simplified manufacturing procedures may reduce manufacturing costs.

[0070] In known arrangements using studs adhered to a patterning device, the total contact area between the studs and the patterning device is relatively small. Therefore, typically, the area of ​​the patterning device surface that contacts each stud is etched to form a stud placement pad. In contrast, the area of ​​the patterning device surface that is affixed to the pellicle frame in a mask assembly according to the twelfth aspect of the present invention is typically much larger than the total area of ​​the patterning device that is affixed to the studs in alternative designs of mask assemblies that use studs. Therefore, advantageously, in a mask assembly according to the twelfth aspect of the present invention, selective etching of the patterning device surface is not required (as may be required in the above alternative designs of mask assemblies to improve adhesion between the patterning device and one or more studs provided thereon). Advantageously, this can reduce the manufacturing time and costs of a mask assembly according to the twelfth aspect of the present invention.

[0071]

[0071] Due to the material properties of PMMA glue, particularly its elasticity, and the dimensions to which it can be applied, deformation of the patterning device due to curing of the PMMA glue is relatively small (compared to other glues). In contrast, if known epoxy glues were used to directly attach a pellicle frame to a patterning device, deformation of the patterning device due to curing of the epoxy glue would be significantly larger, resulting in errors in the pattern projected onto a substrate by a lithography apparatus. Therefore, by using PMMA glue to overcome the problems associated with the use of known epoxy glues, it is possible to produce an improved mask assembly in accordance with a twelfth aspect of the present invention.

[0072]

[0072] PMMA glue is more easily removable than known epoxy glues and is relatively resilient, which advantageously allows for easier replacement of the pellicle assembly forming part of the mask assembly according to the twelfth aspect of the invention.

[0073] It will be appreciated that one or more aspects or features described above or referred to in the following description may be combined with one or more other aspects or features. [Brief explanation of the drawings]

[0074]

[0074] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0075] [Figure 1] 1 depicts a schematic diagram of a lithography system comprising a lithographic apparatus and a radiation source; [Figure 2] 1 is a schematic illustration of various devices and lithographic apparatus according to embodiments of the present invention; [Figure 3] 1 is a perspective view of a mask assembly according to one embodiment of the present invention; [Figure 4] FIG. 4 is a cross-sectional view of a portion of the mask assembly of FIG. 3. [Figure 5] 4 shows an engagement mechanism forming part of the mask assembly of FIG. 3; [Figure 6] 1 illustrates a schematic diagram of a pellicle frame mounting apparatus in accordance with one embodiment of the present invention. [Figure 7] 1 illustrates a pellicle assembly handling system in accordance with one embodiment of the present invention. [Figure 8] 1 illustrates a patterning device handling system according to one embodiment of the present invention; [Figure 9] 9 illustrates a mechanism for the handling system shown in FIGS. 7 and 8 according to one embodiment of the present invention. [Figure 10] 1 illustrates an optical system according to one embodiment of the present invention. [Figure 11] 1 illustrates an optical system according to another embodiment of the present invention. [Figure 12] FIG. 2 is a perspective view of a portion of the pellicle frame mounting device. [Figure 13] 1 shows a portion of the pellicle frame mounting device in more detail. [Figure 14]10 illustrates a schematic representation of the interrelationship between different parts of a pellicle frame mounting apparatus. [Figure 15] 10A and 10B are schematic diagrams illustrating the operation of an engagement mechanism of a pellicle frame mounting device. [Figure 16] 10A and 10B are schematic diagrams illustrating the operation of an engagement mechanism of a pellicle frame mounting device. [Figure 17] 10 shows in more detail the operation of the engagement mechanism of the pellicle frame mounting device. [Figure 18] 1 illustrates schematically a stud mounting device according to one embodiment of the present invention; [Figure 19] 1 shows a cross section of a portion of a stud mounting device. [Figure 20] 20 shows in cross section a variation of the stud mounting arrangement shown in FIG. [Figure 21] This demonstrates how to attach two objects to each other using a poly(methyl methacrylate)-based adhesive. [Figure 22] 1 shows two designs of a mask assembly according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0076] Figure 1 shows a lithography system. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation B. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a mask assembly 15 including a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. If this is the case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0077]

[0076] The source SO, the illumination system IL and the projection system PS may all be constructed and arranged so as to be isolated from the external environment. A gas (e.g. hydrogen) at a pressure below atmospheric pressure may be provided in the source SO. A vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0078] The radiation source SO shown in Figure 1 is of a type that can be referred to as a laser produced plasma (LPP) source. A laser 1, for example a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn), provided by a fuel emitter 3. Although the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in liquid form or may be, for example, a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. Deposition of the laser energy on the tin generates a plasma 7 in the plasma formation region 4. During de-excitation and recombination of the plasma ions, radiation including EUV radiation is emitted from the plasma 7.

[0079] The EUV radiation is collected and focused by a near-normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). Collector 5 may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two elliptical foci. The first focus may be at the plasma formation region 4 and the second focus may be at an intermediate focus 6, as discussed below.

[0080]

[0079] In other embodiments of the laser-produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector configured to receive the EUV radiation at a grazing incidence angle and to focus the EUV radiation to an intermediate focus. The grazing incidence collector may for example be a nested collector comprising multiple grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically about the optical axis.

[0081]

[0080] The radiation source SO may include one or more contamination traps (not shown). For example, the contamination traps may be located between the plasma formation region 4 and the radiation collector 5. The contamination traps may, for example, be rotating foil traps or any other suitable form of contamination trap.

[0082]

[0081] Laser 1 may be separate from radiation source SO. If this is the case, laser beam 2 may be passed from laser 1 to radiation source SO by a beam delivery system (not shown), which may include, for example, appropriate directing mirrors and / or beam expanders and / or other optics. Laser 1 and radiation source SO may be considered together as a radiation system.

[0083]

[0082] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 to form an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 in a closing structure 9 of the radiation source SO.

[0084]

[0083] The radiation beam B travels from the radiation source SO into an illumination system IL that is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together, the facetted field mirror device 10 and the facetted pupil mirror device 11 impart a desired cross-sectional shape and a desired angular distribution to the radiation beam B. The radiation beam B exits the illumination system IL and is incident on a mask assembly 15 that is held by a support structure MT. The mask assembly 15 includes a patterning device MA and a pellicle 19 that is held in place by a pellicle frame 17. The patterning device MA reflects and imparts a pattern to the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0085] After reflecting from the patterning device MA, the patterned radiation beam B is incident on a projection system PS. The projection system comprises a number of mirrors that are configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS is able to apply a demagnification factor to the radiation beam to form images of features that are smaller than corresponding features on the patterning device MA. For example, a demagnification factor of 4 may be applied. In Figure 1, the projection system PS has two mirrors, but the projection system may include any number of mirrors (for example 6 mirrors).

[0086]

[0085] The lithographic apparatus can, for example, be used in scan mode. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the substrate W (i.e. dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the de-magnification and image reversal characteristics of the projection system PS. The patterned radiation beam that is incident on the substrate W may comprise a band of radiation. This band of radiation may be referred to as the exposure slit. During a scan exposure, the substrate table WT and the support structure MT may be moved such that the exposure slit is progressed over an exposure field of the substrate W.

[0087]

[0086] The source SO and / or the lithographic apparatus shown in Figure 1 may include components that are not shown. For example, a spectral filter may be provided in the source SO. The spectral filter may be substantially transparent to EUV radiation but may substantially block radiation of other wavelengths, such as infrared radiation.

[0088] In other embodiments of the lithography system, the source SO may take other forms. For example, in an alternative embodiment, the source SO may include one or more free electron lasers. The one or more free electron lasers may be configured to emit EUV radiation that may be provided to one or more lithography apparatus.

[0089] As briefly mentioned above, mask assembly 15 includes a pellicle 19 disposed adjacent to patterning device MA. Pellicle 19 is disposed in the path of radiation beam B such that radiation beam B passes through pellicle 19 both as it approaches patterning device MA from illumination system IL and as it is reflected by patterning device MA towards projection system PS. Pellicle 19 includes a thin film that is substantially transparent to EUV radiation (but absorbs small amounts of EUV radiation). As used herein, an EUV-transparent pellicle or a film that is substantially transparent to EUV radiation means that pellicle 19 is transmissive to at least 65% of EUV radiation, preferably at least 80%, and more preferably at least 90% of EUV radiation. Pellicle 19 functions to protect patterning device MA from particle contamination.

[0090] Despite efforts to maintain a clean environment inside the lithographic apparatus LA, particles may be present inside the lithographic apparatus LA. Without the pellicle 19, particles could accumulate on the patterning device MA. Particles on the patterning device MA could adversely affect the pattern imparted to the radiation beam B and, in turn, the pattern transferred onto the substrate W. The pellicle 19 provides a barrier between the patterning device MA and the environment within the lithographic apparatus LA to prevent particles from accumulating on the patterning device MA.

[0091]

[0090] Pellicle 19 is positioned a sufficient distance from the patterning device MA so that particles incident on the surface of pellicle 19 are not in the field plane of lithographic apparatus LA. This separation between pellicle 19 and patterning device MA acts to prevent particles on the surface of pellicle 19 from imparting a pattern to the radiation beam B that is imaged onto substrate W. It will be appreciated that even if a particle is present in radiation beam B, if its position is not in the field plane of radiation beam B (i.e. not at the surface of patterning device MA), the image of this particle will be out of focus at the surface of substrate W. Barring other considerations, it may be desirable to position pellicle 19 at a significant distance from the patterning device MA. In practice, however, the presence of other components in lithographic apparatus LA limits the space available to accommodate a pellicle. In some embodiments, the separation between pellicle 19 and patterning device MA may be, for example, between about 1 mm and 10 mm, such as between 1 mm and 5 mm, more preferably between 2 mm and 2.5 mm.

[0092] A mask assembly can be prepared for use in a lithographic apparatus by attaching a pellicle to a pellicle frame and attaching the pellicle frame to a patterning device. A mask assembly comprising a patterning device MA and a pellicle supported by a pellicle frame adjacent to the patterning device can be prepared remotely from the lithographic apparatus LA, and the mask assembly can be transported to the lithographic apparatus LA for use in the lithographic apparatus LA. For example, at a location where a pattern is to be imparted to the patterning device, the pellicle frame supporting the pellicle can be attached to the patterning device to form a mask assembly. The mask assembly can then be transported to another location where the lithographic apparatus LA is located and provided to the lithographic apparatus LA for use in the lithographic apparatus LA.

[0093]

[0092] A mask assembly, with a pellicle held in place by a pellicle frame, is fragile, and transporting the mask assembly can present a risk of damaging the pellicle. Furthermore, assembling the mask assembly in an environment separate from the lithography apparatus LA can result in exposing the mask assembly to a variety of pressure conditions. For example, the mask assembly may be transported to the lithography apparatus under ambient pressure conditions. The mask assembly may then be loaded into the lithography apparatus LA via a load lock that is pumped to vacuum pressure conditions. Changes in the pressure conditions to which the mask assembly is exposed can create pressure differences in the pellicle, which can cause the pellicle to bend and risk damaging the pellicle. In one embodiment, the lithography system can include a lithography apparatus LA connected to a pellicle frame mounting apparatus. If this is the case, the mask assembly, including the mask and pellicle, can be transported directly from the pellicle frame mounting apparatus to the lithography apparatus while maintaining a controlled environment (e.g., a vacuum environment).

[0094] FIG. 2 is a schematic diagram of an apparatus suitable for assembling a mask assembly 15 and transferring the mask assembly to a lithographic apparatus LA. FIG. 2 shows a pellicle mounting apparatus 855 that can be used to mount a pellicle 19 on a pellicle frame 17, and a pellicle assembly transport device 881 that can be used to transport the pellicle assembly. Also shown is a stud mounting apparatus 840 that can be used to mount studs 51 on a patterning device MA. The studs 51 allow the pellicle frame 17 (and pellicle 19) to be releasably mounted on the patterning device MA. Also shown is a mask transport device 880 that can be used to transport the mask with the studs attached. Also shown is a pellicle frame mounting apparatus 857 that can be used to form the mask assembly 15 by mounting the pellicle frame 17 (and pellicle 19) on the patterning device MA. Also shown is a mask assembly transport device 853 that can be used to transport the mask assembly 15 from the pellicle frame mounting apparatus 857 to the lithographic apparatus LA.

[0095] Pellicle mounting apparatus 855 may be located at a location different from where lithographic apparatus LA is located. Stud mounting apparatus 840 may be located at a location different from where lithographic apparatus LA is located. Alternatively, one or both of pellicle mounting apparatus 855 and stud mounting apparatus 840 may be located at the same location (e.g., within a lithography manufacturing facility) as where lithographic apparatus LA is located.

[0096] The pellicle mounting device 855 receives the pellicle 19, the pellicle frame 17, and an engagement mechanism (not shown). The pellicle 19 and the pellicle frame 17 can be manually placed into the pellicle mounting device 855. Glue is applied to the engagement mechanism-receiving openings of the pellicle frame 17 (e.g., at locations described further below). Application of the glue can be manual or automated (or partially automated).

[0097]

[0096] The engagement mechanism and pellicle frame 17 are aligned with respect to one another (eg, using an optical alignment device), and then the engagement mechanism is inserted into the opening in the pellicle frame 17.

[0098]

[0097] Glue is also applied to the pellicle frame 17 (e.g., at spaced locations around the periphery of the pellicle frame 17). Application of the glue can be manual or automated (or partially automated). An optical alignment system is used to align the pellicle 19 with respect to the pellicle frame 17, and then the pellicle is pressed against the pellicle frame.

[0099] The pellicle 19 can be manipulated by a pellicle manipulation section forming part of the pellicle mounting apparatus 855. The pellicle manipulation section can include means for applying tension to the pellicle 19. The pellicle manipulation section can secure the pellicle 19 to the pellicle frame 17 by applying tension to the pellicle 19 at room temperature for a period of time sufficient for the glue to cure, and then pressing the pellicle 19 against the pellicle frame 17. The pressure on the pellicle 19 is then removed. An additional cure of the glue is then performed at elevated temperature using a curing oven (which can form part of the pellicle mounting apparatus 855). This also cures the glue that attaches the engagement mechanism to the pellicle frame 17. In an alternative approach, the glue can be cured by applying some heat (rather than curing at room temperature) while the pellicle 19 is pressed against the pellicle frame.

[0100]

[0099] The glue can be provided by a glue dispenser. The glue dispenser can form part of the pellicle mounting device 855. The glue dispenser can include a syringe. The syringe can dispense a predetermined amount of one or more components of the glue. The glue dispenser can include a nozzle. For example, a nozzle can be connected to a syringe, and the syringe connected to the nozzle can be used to provide one or more components of the glue. The glue can be applied using a cylindrical nozzle. The glue can be applied using a tapered nozzle. The glue dispenser can include a brush, and the brush can be used to apply one or more components of the glue. The glue dispenser can include a sponge, and the sponge can be used to apply one or more components of the glue. The glue dispenser can include a printing device (e.g., a screen printing device) for providing one or more components of the glue. The glue dispenser can include a dispensing device for providing one or more components of the glue as a spray (e.g., an aerosol spray dispensing system can be used). It will be appreciated that the glue may be provided in any known manner.

[0101] [000100] A glue dispenser can provide a multi-component glue (e.g., a glue accelerator and an initiator). One component of the glue can have a higher viscosity than another component of the glue. That is, there can be a glue component with a relatively high viscosity (a "thick" component) and a glue component with a relatively low viscosity (a "thin" component). In an exemplary embodiment, the glue dispenser can apply the thick glue component using a syringe and nozzle. In an exemplary embodiment, the glue dispenser can apply the thin glue component using a brush, sponge, screen printing device, or aerosol spray dispensing system.

[0102] [000101] Although glue is described above as being used to attach pellicle 19 to pellicle frame 17, any suitable type of bond (including no glue) may be used to attach the pellicle to the pellicle frame.

[0103] [000102] The resulting pellicle assembly 16 is inspected using a particle inspection tool, which may form part of the pellicle mounting apparatus 855 (or may be a separate tool). The particle inspection tool may be configured to inspect the pellicle 19 and / or the pellicle frame 17 for particles. The particle inspection tool may, for example, reject a pellicle assembly 16 having more particles than a given particle threshold. The particle inspection tool may also be used to inspect the pellicle 19 and / or the pellicle frame 17 before the pellicle and pellicle frame are glued together.

[0104] [000103] Pellicle mounting apparatus 855 can be configured to seal pellicle assembly 16 in pellicle assembly transport device 881 (a sealed box) after inspection. As shown, pellicle assembly transport device 881 can be positioned to hold the pellicle assembly in an orientation such that pellicle 19 is below pellicle frame 17. Because transport device 881 is sealed, it can transport pellicle assembly 16 without contaminating it. Pellicle assembly 16 can be transferred in transport device 881 to pellicle frame mounting apparatus 857.

[0105] [000104] The pellicle mounting apparatus 855 includes a clean environment to reduce the number of particles within the sealed environment, thereby reducing the number of particles that can deposit on the pellicle 19. The pellicle mounting apparatus 855 can be located, for example, at the location where the pellicle is manufactured. In some embodiments, the pellicle 19 can be provided to the pellicle mounting apparatus 855 directly from a pellicle manufacturing tool (not shown) where the pellicle 19 is manufactured. The pellicle 19 can be provided to the pellicle mounting apparatus 855 from the pellicle manufacturing tool, for example, while being held within a clean environment. This reduces the possibility of contaminating or damaging the pellicle 19 before providing it to the pellicle mounting apparatus 855. The clean environment can be, for example, a sealed environment (i.e., completely isolated from the outside environment). The sealed environment can be pumped to maintain a vacuum within the sealed environment.

[0106] [000105] The attachment of pellicle 19 to pellicle frame 17 can be controlled to achieve a desired tension in pellicle 19. For example, the tension in pellicle 19 can be measured during or after attachment of pellicle 19 to pellicle frame 17, and the tension can be adjusted accordingly to achieve the desired tension in pellicle 19. Tension in pellicle 19 can be maintained, for example, by applying an outward force to components of pellicle frame 17 to stretch pellicle 19. Tension in pellicle 19 can be maintained, for example, by using the difference in the coefficients of thermal expansion between the pellicle frame and the pellicle.

[0107] [000106] In one embodiment, the patterning device (which may be referred to as a mask) MA may be provided with protrusions that are received by an engagement mechanism (e.g., as described further below). The patterning device may receive, for example, four protrusions (referred to herein as studs). As shown in Figure 2, stud attachment apparatus 840 may be used to attach studs 51 to the patterning device MA.

[0108] [000107] The studs 51 and patterning device MA can be manually placed into the stud fitting apparatus 840. The patterning device MA can be held in a controlled environment 841, which is separated from the rest of the stud fitting apparatus 840. This separation can be achieved by a partition 842 with openings through which the studs 51 can protrude to contact the patterning device MA. The controlled environment 841 can be held at a higher pressure than the rest of the stud fitting apparatus 840 (e.g., by pumping gas through an outlet in the controlled environment). This reduces or prevents the ingress of contaminant particles from the rest of the stud fitting apparatus into the controlled environment 841.

[0109] [000108] The stud attachment apparatus 840 may include a stud handling mechanism (not shown), such as a robot or actuator, for accurately placing the studs. An example of an actuator suitable for placing studs on the patterning device is a Lorentz actuator (not shown). The stud attachment apparatus 840 may also include a device for automatically providing a given amount of glue or adhesive to the surface of the stud to be attached to the patterning device MA. Application of the glue or adhesive may also be performed manually. Contamination of the patterning device MA by contaminants from the glue or adhesive is prevented or reduced by airflow from the controlled environment 841 above the partition 842 to below the partition (this airflow is caused by the pressure above the partition being higher than the pressure below the partition).

[0110] [000109] The stud mounting apparatus 840 may further include an optical alignment system for aligning the studs with respect to alignment markers present on the reticle in order to accurately position the studs. For example, alignment markers conventionally provided on the patterning device MA and used for pattern alignment may also be used for aligning the studs.

[0111] [000110] The stud mounting arrangement may include a support structure that is movable in the XYZ and Rz directions to adjust the position of the patterning device MA. The position of the support structure holding the patterning device MA may be adjusted manually by coarse and fine mechanical adjustment devices, or using automated (or semi-automated) actuators, or any other type of device suitable for alignment and positioning that is coupled to the patterning device table.

[0112] [000111] Once the studs 51 and patterning device MA are aligned, the studs 51 are pressed against the patterning device MA. The studs 51 can be secured to the mask MA by pressing them against the patterning device MA at room temperature for a period of time sufficient for the glue to harden. Alternatively, the studs 51 may be heated to accelerate the hardening of the glue. An additional hardening of the glue is then carried out at elevated temperature using a curing oven (which may form part of the stud mounting apparatus 840).

[0113] [000112] The glue can be provided by a glue dispenser. The glue dispenser can form part of the stud attachment device 840. The glue dispenser can include a syringe. The syringe can dispense a predetermined amount of one or more components of the glue. The glue dispenser can include a nozzle. For example, a nozzle can be connected to a syringe, and the syringe connected to the nozzle can be used to provide one or more components of the glue. The glue can be applied using a cylindrical nozzle. The glue can be applied using a tapered nozzle. The glue dispenser can include a brush, and the brush can be used to apply one or more components of the glue. The glue dispenser can include a sponge, and the sponge can be used to apply one or more components of the glue. The glue dispenser can include a printing device (e.g., a screen printing device) to provide one or more components of the glue. The glue dispenser can include a dispensing device to provide one or more components of the glue as a spray (e.g., an aerosol spray dispensing system can be used). It will be appreciated that the glue may be provided in any known manner.

[0114] [000113] A glue dispenser can provide a multi-component glue (e.g., a glue accelerator and an initiator). One component of the glue can have a higher viscosity than another component of the glue. That is, there can be a glue component with a relatively high viscosity (a "thick" component) and a glue component with a relatively low viscosity (a "thin" component). In an exemplary embodiment, the glue dispenser can apply the thick glue component using a syringe and nozzle. In an exemplary embodiment, the glue dispenser can apply the thin glue component using a brush, sponge, screen printing device, or aerosol spray application system.

[0115] [000114] The patterning device MA and studs 51 may be inspected using a particle inspection tool (which may form part of the stud mounting arrangement 840).

[0116] [000115] The stud mounting apparatus 840 encloses the patterning device MA and studs 51 within a mask transfer device 880 (a sealed box). Because the mask transfer device 880 is sealed, the patterning device MA and studs 51 can be transferred without contaminating the mask MA. The patterning device MA and studs can be transferred within the mask transfer device 880 to the pellicle frame mounting apparatus 857.

[0117] [000116] In one embodiment, the mask MA is provided in a sealed box to the stud attachment apparatus 840 (to reduce the risk of contamination), and the box remains sealed until just before attachment of the studs 51 to the patterning device MA, thereby minimizing the time during which contamination can transfer to the mask MA.

[0118] [000117] Part of the controlled environment 841 of the stud mounting apparatus 840 may be provided by an enclosure which later forms part of the patterning device MA transfer device 880 (sealed box). The enclosure may form the walls and roof of the mask transfer device 880. The floor of the mask transfer device 880 is formed by a plate which is fitted after (e.g. immediately after) the studs 51 have been mounted. Using an enclosure in this way helps to prevent contamination from entering the patterning device MA. The enclosure may comprise a cover for a pod. The mask table of the stud mounting apparatus 840 may be configured to receive the enclosure.

[0119] Similarly, part of the pellicle mounting apparatus 855 may be formed by a housing that subsequently forms part of the pellicle assembly transport device 881 .

[0120] [000119] Both the pellicle assembly 16 in the pellicle assembly transfer device 881 and the patterning device MA (and studs 51) in the mask transfer device 880 are transferred to a pellicle frame mounting apparatus 857. The pellicle frame mounting apparatus 857 may be provided in a manufacturing facility where one or more lithographic apparatus are also provided.

[0121] [000120] Pellicle frame mounting apparatus 857 is configured to mount pellicle frame 17 of pellicle assembly 16 to studs 51 on patterning device MA to form mask assembly 15. Pellicle frame mounting apparatus 857 may include a controlled environment 860 that is separated from the rest of pellicle frame mounting apparatus 857. This separation may be achieved by a partition 862 with an opening through which a handler extends (not shown in FIG. 2). The handler may be operated by control system 870 (described further below). Controlled environment 860 may be maintained as a clean environment to reduce the number of particles within the controlled environment, thereby reducing the number of particles that may deposit on mask assembly 15. Controlled environment 860 may be held at a higher pressure than the rest of pellicle frame mounting apparatus 857 (e.g., by delivering gas through an outlet in controlled environment 860). This reduces or prevents the ingress of contaminant particles from other portions of the pellicle frame mounting apparatus 857 into the controlled environment 860 .

[0122] [000121] The mask assembly 15 assembled by the pellicle frame mounting apparatus 857 is transferred from the pellicle frame mounting apparatus 857 to the lithographic apparatus LA in the mask assembly transfer device 853. The mask assembly transfer device 853 may include a sealed clean environment in which the mask assembly 15 is transferred, thereby reducing the chance of contamination or damage to the mask assembly 15 during transfer. The sealed clean environment may be, for example, pumped to a vacuum.

[0123] [000122] Pellicle assembly 16 can be loaded, unloaded or reloaded onto patterning device MA using pellicle frame mounting apparatus 857. Pellicle frame mounting apparatus 857 may include an operating portion arranged to operate an engagement mechanism of pellicle frame 17 (described further below).

[0124] [000123] The patterning device MA may, for example, be provided with alignment marks. The pellicle frame 17 may be positioned relative to the alignment marks on the patterning device MA. Aligning the pellicle frame 17 relative to the alignment marks on the patterning device MA has the advantage of improving the accuracy with which the pellicle frame 17 is positioned on the patterning device MA during attachment of the pellicle frame 17 to the patterning device MA.

[0125] [000124] In some embodiments, the patterning device MA may be cleaned in the pellicle frame mounting apparatus 857, for example to remove particles from the patterning device MA. In other embodiments, cleaning of the patterning device MA may be performed in a dedicated cleaning tool.

[0126] [000125] While the illustrated embodiment shows the pellicle frame 17 attached to the front surface of the mask MA, in other embodiments, the pellicle frame 17 may be attached to other portions of the mask MA. For example, the pellicle frame 17 may be attached to the side surface of the mask MA. This may be achieved, for example, using sub-mounts that provide releasably engageable attachment between the pellicle frame 17 and the side surface of the mask MA. In alternative embodiments, the pellicle frame 17 may be attached to the mask MA using a combination of some attachment locations on the side surface of the mask MA and some attachment locations on the front surface of the mask MA. Attachment may be provided, for example, by sub-mounts that releasably engage the pellicle frame 17 with the mask MA.

[0127] [000126] In some embodiments, the pellicle frame mounting device 857 may include a particle inspection tool (not shown). The particle inspection tool may be configured to inspect the mask assembly 15 for particles present on the mask assembly 15. The particle inspection tool may, for example, reject a mask assembly 15 that has more particles deposited thereon than a given particle threshold.

[0128] [000127] In some embodiments, the pellicle frame mounting apparatus 857 may include a pattern inspection system that inspects the pattern on the patterning device MA for defects. The pattern inspection system may inspect the pattern on the patterning device MA before and / or after mounting the pellicle frame 17 to the patterning device MA.

[0129] [000128] The attachment of pellicle frame 17 to patterning device MA can be controlled to achieve a desired tension in pellicle 19. For example, the tension in pellicle 19 can be measured during attachment of pellicle frame 17 to patterning device MA, and the tension can be adjusted in response to this measurement to achieve the desired tension in pellicle 19.

[0130] The lithographic apparatus LA may, for example, correspond to the lithographic apparatus LA shown in FIG. 1 . The lithographic apparatus LA may include components configured to receive a mask assembly 15 from a mask assembly transport device 853 and load the mask assembly 15 onto a support structure MT of the lithographic apparatus LA. The mask assembly 15 may be illuminated with a conditioned radiation beam B provided by an illumination system IL. A patterning device MA of the mask assembly 15 may impart the conditioned radiation beam B with a pattern in its cross-section to form a patterned radiation beam. The patterned radiation beam may be projected by a projection system PS onto a substrate W held on a substrate table WT. The conditioned radiation beam may, for example, comprise EUV radiation. In an embodiment in which the conditioned radiation beam comprises EUV radiation, a pellicle 19 of the mask assembly 15 may be substantially transparent to EUV radiation.

[0131] In some embodiments, the pellicle assembly 16 can be mounted to the patterning device MA to form the mask assembly 15 in a vacuum environment within the pellicle frame mounting arrangement 857. The mask assembly 15 can then be transferred to the lithographic apparatus LA in a vacuum environment by the mask assembly transport device 853 and held under vacuum conditions within the lithographic apparatus LA. The mask assembly 15 can therefore be exposed to substantially the same pressure conditions throughout its assembly within the pellicle frame mounting arrangement 857 and its use within the lithographic apparatus LA. This has the advantage of reducing pressure changes to which the mask assembly 15 is exposed, and therefore reducing pressure differences that may occur across the pellicle 19.

[0132] [000131] In some embodiments, the patterning device MA and / or pellicle 19 can be inspected for particles and / or defects while the components are held in vacuum in pellicle frame mounting arrangement 857. Advantageously, the patterning device MA and / or pellicle 19 are therefore inspected under pressure conditions similar to those to which they will be exposed during use in lithographic apparatus LA. This is advantageous because the pellicle frame mounting arrangement 857 can detect any particles that may be deposited on the patterning device MA and / or pellicle while pumping to vacuum conditions.

[0133] [000132] In some embodiments, the lithography system may further include a separate inspection apparatus (not shown) configured to inspect one or more components of the mask assembly 15 for particles and / or defects. The mask assembly 15 may be transferred to the inspection apparatus (e.g., by the mask assembly transfer device 853) after, for example, assembly in the pellicle frame mounting apparatus 857 and before transfer to the lithography apparatus LA.

[0134] [000133] The above-described embodiments of the present invention have the advantage that the mask assembly 15 can be assembled and delivered to the lithographic apparatus LA in an automated (or semi-automated) process. The assembly and transfer of the mask assembly 15 can all be performed in a sealed, clean environment that can be pumped to, for example, vacuum pressure conditions. This reduces the chance of components of the mask assembly 15 being contaminated or damaged prior to use of the mask assembly 15 in the lithographic apparatus LA.

[0135] [000134] Generally, the useful life of pellicle 19 may be shorter than the useful life of the patterning device MA. Therefore, it may be desirable to remove pellicle assembly 16 from patterning device MA and replace it with a new pellicle assembly to allow continued use of the patterning device MA. Replacing pellicle assembly 16 can be performed, for example, in pellicle frame mounting apparatus 857. After use, for example, in lithographic apparatus LA, mask assembly 15 can be returned to pellicle frame mounting apparatus 857 using mask assembly transfer device 853 for replacing the pellicle assembly in pellicle frame mounting apparatus 857. After removing pellicle assembly 16, a cleaning process can be performed on the patterning device MA to remove contamination from the patterning device MA. Before performing a cleaning process on the patterning device, studs 51 can be removed from the patterning device MA.

[0136] It should be noted that during the various operations shown in FIG. 2 , the patterned side of the patterning device MA faces downwards. Keeping the patterned side of the patterning device MA facing downwards is advantageous as it reduces the chance of contaminant particles being incident on the pattern. Larger contaminant particles tend to fall downwards due to gravity and therefore enter the other side of the mask. Smaller contaminant particles are less affected by gravity but may instead be affected by other transport physics. Apparatus according to embodiments of the invention may include devices aimed at addressing this. For example, the apparatus may include an ionizer to remove static charge, thereby reducing the risk of static electricity sticking particles to the pellicle.

[0137] 3-5 illustrate a mask assembly. The pellicle frame 17 and pellicle 19 are suspended relative to the patterning device MA. The pellicle frame 17 can be releasably engaged with the patterning device MA. The releasable engagement is provided by a mount including multiple submounts 10 (e.g., two, three, four, or more submounts). This mount allows for easy and convenient removal of the pellicle frame 17 (and pellicle 19) from the patterning device MA. Removal of the pellicle frame 17 and pellicle 19 from the patterning device MA can be clean, i.e., substantially free of contaminant particles. Once the pellicle frame 17 is removed from the patterning device MA, the patterning device MA can be inspected (and cleaned, if necessary) using an inspection tool. The pellicle frame 17 and pellicle 19 can then be easily reattached to the patterning device MA or replaced with a new pellicle frame 17 and pellicle 19. Each submount 10 of the mount is formed with engagement features and protrusions (described in more detail below with reference to FIG. 4).

[0138] 3, the pellicle 19 is attached to the pellicle frame 17. The pellicle 19 may be glued to the pellicle frame 17, for example. Four engagement features 50A-50D are provided on the pellicle frame 17. Each of the engagement features 50A-50D is provided on an inclined portion 49A-49D. The inclined portions 49A-49D are generally trapezoidal in shape. The inclined portions 49A-49D are attached to the pellicle frame 17 and protrude from the pellicle frame 17 within a major surface of the pellicle frame 17. Each of the engagement features 50A-50D is configured to receive a protrusion 51 (which may be referred to as a stud 51, for example) extending from the patterning device MA (described below in connection with FIG. 4). Two engagement features 50A and 50B are provided on one side of the pellicle frame 17, and two engagement features 50C and 50D are provided on the opposite side of the pellicle frame 17. Other combinations are possible, such as providing one engagement feature 50 on each of the four frame sides. Engagement features 50A-50D are provided on sides of pellicle frame 17 that face in the scanning direction (denoted in FIG. 3 as the y-direction, according to conventional notation) during use in lithography apparatus LA. However, engagement features 50A-50D may also be provided on sides of pellicle frame 17 that face perpendicular to the scanning direction (denoted in FIG. 3 as the x-direction, according to conventional notation) during use in lithography apparatus LA.

[0139] [000138] The protrusions 51 received by the engagement features 50A-50D may be positioned on the front surface of the patterning device MA. Additionally or alternatively, the protrusions 51 may be positioned on the sides of the patterning device MA. The protrusions 51 may extend upward from the sides of the patterning device MA. In such an arrangement, each of the protrusions 51 may have a flat lateral surface to facilitate secure attachment to the sides of the patterning device MA.

[0140] [000139] FIG. 3 shows four engagement mechanisms 50A-50D fixed to the pellicle frame 17. Two of the engagement mechanisms 50A, 50D are configured to move in the y direction (i.e., provide flexibility or compliance in the y direction). Two of the engagement mechanisms 50B, 50C are configured to move in the x direction (i.e., provide flexibility or compliance in the x direction). However, because all four engagement mechanisms 50A-50D are configured to achieve engagement between the engagement mechanisms 50A-50D and the protrusions 51 (not shown) through movement in the y direction, as can be seen in the figure, all four engagement mechanisms 50A-50D include engagement arms 80 extending in the y direction. A potential drawback of this configuration is that sudden deceleration during y-direction scanning movement (due to the inertia of the pellicle frame 17) can cause the engagement mechanisms 50A-50D to slide and become disengaged from the protrusions. This can occur, for example, in the event of a "crash" of the mask support structure (see FIG. 1). In an alternative arrangement, all four engagement mechanisms 50A-50D may include engagement arms 80 that extend in the x-direction (i.e., non-scanning direction). Having all of the engagement arms 80 extend in the non-scanning direction advantageously avoids the possibility that a sudden y-direction deceleration could cause the engagement mechanisms 50A-50D to disengage. In general, all of the engagement arms 80 of each engagement mechanism 50A-50D may extend in substantially the same direction.

[0141] To allow movement / flexibility in the x direction, the arms 62 supporting the locking members of the two engagement mechanisms 50B, 50C extend in the y direction. These arms 62 are elastically flexible in the x direction, thereby providing movement / flexibility in the x direction. Accordingly, the engagement arms 80 of the two engagement mechanisms 50B, 50C extend generally parallel to the arms 62 of these engagement mechanisms. To allow movement / flexibility in the y direction, the arms 62 supporting the locking members of the other two engagement mechanisms 50A, 50D extend in the x direction. These arms 62 are elastically flexible in the y direction, thereby providing movement / flexibility in the y direction. Accordingly, the engagement arms 80 of the two engagement mechanisms 50A, 50D extend generally perpendicular to the arms 62 of these engagement mechanisms. The movement / flexibility provided by the engagement mechanisms 50A-50D allows the pellicle frame 17 to flex relative to the patterning device MA as needed when temperature changes occur. This is advantageous because it avoids the creation of potentially damaging thermal stresses in the pellicle frame 17 .

[0142] [000141] Engagement features 50A-50D in Figure 3 are illustrated with tabs 56 having a different configuration than tabs 56 shown in Figure 5. However, tabs 56 provide the same function of facilitating engagement between engagement features 50A-50D and pellicle frame 17. Any suitable configuration of tabs 56 may be used.

[0143] 4 shows one engagement feature 50A in cross section with a protrusion 51 protruding from the patterning device MA. Engagement feature 50A and protrusion 51 together comprise submount 10. Protrusion 51, which may be referred to as a stud, may be attached to the patterning device MA, for example, by glue or other bonding means (such as optical contact, magnetic, or van der Waals forces). Protrusion 51 comprises a distal head 53 positioned on a shaft 55 extending from a base 57. Base 57 is fixed to the patterning device MA, for example, using glue. Shaft 55 and distal head 53 may be cylindrical or have any other suitable cross-sectional shape.

[0144] [000143] Submount 10 suspends pellicle frame 17 relative to patterning device MA such that a gap G (which can be considered a slit) exists between pellicle frame 17 and patterning device MA. Gap G may be maintained by engagement between cap 66 of engagement mechanism 50A and distal head 53 of protrusion 51 (or by some other movement-limiting component). Gap G may be wide enough to equalize pressure between the external environment and the space between pellicle 19 and patterning device MA. Gap G may also be narrow enough to provide a desired restriction on the route by which contaminant particles can enter the space between pellicle 19 and patterning device MA from the external environment. Gap G may be, for example, at least 100 microns to equalize pressure between the external environment and the space between pellicle 19 and patterning device MA. Gap G may be, for example, less than 500 microns, more preferably less than 300 microns. Gap G may be, for example, between 200 microns and 300 microns.

[0145] [000144] Figure 5 shows the submount 10 of Figure 4 in more detail (including engagement features 50A and protrusions 51). Pellicle frame 17, which is attached to engagement features 50A, is not shown in Figure 5. Similarly, patterning device MA, from which protrusions 51 protrude, is not shown in Figure 5. Figure 5A shows submount 10 as viewed from below, and Figure 5B shows a perspective view of submount 10 as viewed from below.

[0146] [000145] Engagement mechanism 50A includes a rectangular outer wall 60 that is received in an opening in pellicle frame 17 (see FIG. 3). A pair of arms 62 extend in the y-direction within the space defined by outer wall 60. A connecting member 63 extends between the distal ends of arms 62. Arms 62 are an example of a resilient member. Other resilient members may also be used. Arms 62 and connecting member 63 together form a generally U-shaped support. A locking member 70 is connected to the distal end of the generally U-shaped support. Locking member 70 engages with protrusions 51 (which may be referred to as studs), thereby securing pellicle frame 17 to patterning device MA.

[0147] [000146] Locking member 70 includes a pair of engagement arms 80 provided with engagement tabs 81, and also includes cap 66. As best seen in FIG. 5B, when locking member 70 engages with protrusion 51, engagement tabs 81 press against the underside of distal head 53 of protrusion 51, and cap 66 presses against the outer surface of distal head 53. This pressing of engagement tabs 81 and cap 66 against distal head 53 of protrusion 51 secures engagement mechanism 50A to the protrusion and provides a rigid submount 10, thereby providing a secure connection between pellicle frame 17 and patterning device MA.

[0148] [000147] The cap 66 and engagement arm 80 extend from intermediate arms 82a, 82b. The intermediate arms 82a, 82b extend from connecting member 63 and generally extend in the y direction within the space defined by the outer wall 60. The connecting member 83 extends between the intermediate arms 82a, 82b. Together, the intermediate arms 82a, 82b and connecting member 83 form a generally U-shaped support.

[0149] [000148] Thus, a first generally U-shaped support formed by arms 62 and connecting member 63 extends generally in the y direction within the space defined by outer wall 60, and a second generally U-shaped support formed by support arms 82a, 82b and connecting member 83 extends in the opposite direction within that space.

[0150] [000149] The arms 62 forming the first generally U-shaped support have some flexibility in the x-direction, which allows some movement of the locking members 70 in the x-direction. Therefore, the submount 10 allows some movement of the pellicle frame in the x-direction relative to the patterning device at the submount's location. Because the arms 62 are made of a resilient material, they tend to return to their initial orientation. The submount 10 can be considered a kinematic submount. The arms 62 are significantly thicker in the z-direction than in the x-direction (best seen in FIG. 5B ), resulting in significantly less arm flexion in the z-direction than in the x-direction. Because the arms extend in the y-direction, no significant movement in the y-direction occurs. Thus, the arms 62 can prevent or substantially prevent local movement of the pellicle frame 17 in the y- and z-directions while allowing some movement of the pellicle frame 17 in the x-direction.

[0151] [000150] Cap 66 extends from first support arm 82a. Engagement arm 80 extends from second support arm 82b. First support arm 82a is significantly thicker in the x-direction than arm 62 and therefore does not allow significant movement in the x-direction relative to arm 62. Second support arm 82b has a similar thickness to arm 62 in the x-direction, but movement of second support arm 82b in the x-direction can only occur if first support arm 82a also moves, and such movement of second support arm 82b is restricted by connecting member 83 extending between intermediate arms 82a, 82b.

[0152] [000151] The engagement arm 80 extends from the second support arm 82b generally toward the cap 66. The proximal end of the engagement arm 80 extends along the majority of the second support arm 82b (thereby substantially preventing the engagement arm 80 from bending in a direction generally parallel to the patterned surface of the patterning device MA). The engagement arm 80 tapers as it extends generally toward the cap 66. An engagement tab 81 extends inward from the distal end of the engagement arm 80 to engage with the upper surface of the distal head 53 of the projection 51. A block 54 is provided above the engagement tab 81 to provide an actuator receiving surface, as described further below. The engagement arm 80 is elastically deformable in the z-direction. The engagement arm 80 can be thin enough to bend in the z-direction. Additionally or alternatively, some flexing of the engagement arm 80 in the z direction may be facilitated by a groove 59 extending in the y direction at the point where the engagement arm 80 connects to the support arm 82b.

[0153] [000152] Tabs 56 extend outwardly from outer wall 60. Tabs 56 can be used to secure engagement mechanism 50A to pellicle frame 17. This is shown in Figure 3, although the configuration of tabs 56 is different.

[0154] [000153] One embodiment of a pellicle frame mounting apparatus 857 is shown in Figure 6. The pellicle frame mounting apparatus 857 may correspond to the pellicle mounting apparatus 857 shown in Figure 2. Figure 6 shows the pellicle frame mounting apparatus 857 schematically in cross section. The mask assembly 15 includes a patterning device MA provided with a pellicle frame 17 and a pellicle 19 (not shown). The frame 17 is provided with engagement mechanisms 50 corresponding to the engagement mechanisms 50A-50D described above in connection with Figures 3-5. Pins 1090 of the pellicle frame mounting apparatus 857 protrude through holes 895 in a partition 862. The partition 862 may correspond to or be positioned on the support structure 101. Windows 893 and 894 are positioned on the support structure 101, and imaging sensors 105 and 106 are positioned below the windows 893 and 894. Alignment marks 109 are provided on the windows 893, 894. Alignment marks 704 are also provided on the patterning device MA.

[0155] [000154] Additional support structures 97 are provided around the periphery of the pellicle frame mounting arrangement 857. The additional support structures may have fixed locations (as shown) and are referred to herein as fixed support structures 97. Intermediate support structures 98 are provided on top of the fixed support structures 97. The intermediate support structures 98 extend inwardly from the fixed support structures 97 as shown. The intermediate support structures 98 support both the pellicle frame 17 and the patterning device MA prior to mounting the pellicle frame 17 to the patterning device MA. Contact points 99 between the intermediate support structures 98 and other elements may be kinematic connections, for example. The contact points 99 may be provided with a coating of polyetheretherketone (PEEK).

[0156] [000155] During use, pellicle assembly 16 is loaded into pellicle frame mounting apparatus 857. Pellicle assembly 16 can be transferred to pellicle frame mounting apparatus 857 without exposure to contamination. For example, pellicle assembly transfer device 881 can be received in a load lock or flow controlled environment within pellicle frame mounting apparatus 857, and pellicle assembly 16 can be removed from the transfer device in the load lock or flow controlled environment. Pellicle assembly 16 can then be transferred to the controlled environment 857 above partition 862.

[0157] [000156] For example, a pellicle assembly handling system can be used to position the pellicle assembly 16 relative to the pellicle frame mounting device 857. The pellicle assembly handling system can include a pellicle assembly gripper. FIG. 7 shows an example of a pellicle assembly gripper 400. FIG. 7A shows a top view of the pellicle assembly gripper 400. FIG. 7A also shows a pellicle assembly 16. The pellicle assembly 16 shown in FIG. 7A can correspond to the pellicle assembly 16 shown in FIG. 3. FIG. 7B shows a perspective view of the pellicle assembly gripper 400. The pellicle assembly gripper 400 includes a first arm 402a, a second arm 402b, a plurality of pellicle assembly alignment portions 406, and a plurality of pellicle assembly support pads 408.

[0158] Each of the first arm 402a and the second arm 402b includes a base portion 410 and a grip portion 412. The base portion 410 of each of the first arm 402a and the second arm 402b is movably attached to a pellicle assembly gripper controller 422. Specifically, the base portion 410 of each of the first arm 402a and the second arm 402b is rotatably or pivotally attached to the pellicle assembly gripper controller 422. Each of the first arm 402a and the second arm 402b can be described as being movable between at least an open position and a closed position. A gap 414 between the grip portion 412 of the first arm 402a and the grip portion 412 of the second arm 402b can be varied. The gap 414 can be varied by moving one or both of the first arm 402a and the second arm 402b. The gap 414 is variable using a pellicle assembly gripper control knob 424 that forms part of the pellicle assembly gripper controller 422. The pellicle assembly gripper control knob 424 is configured to change the position and / or rotation of the arms 402 a, 402 b when rotated, thereby changing the gap 414. The pellicle assembly gripper 400 can be described as being in an open or closed configuration. The open configuration of the pellicle assembly gripper 400 can correspond to the gap 414 defined by the first arm 402 a and the second arm 402 b of the pellicle assembly gripper 400 being wider than the gap 414 that exists when the pellicle assembly gripper 400 is in a closed configuration. In FIG. 7 , the pellicle assembly gripper 400 is illustrated in a closed configuration. In the closed configuration of the pellicle assembly gripper 400, the gap 414 is approximately the same size as the outer dimension of the pellicle frame 17. In the open configuration of pellicle assembly gripper 400, gap 414 is larger than the aforementioned outer dimensions of pellicle frame 17.

[0159] The plurality of pellicle assembly alignment portions 406 and the plurality of pellicle assembly support pads 408 are arranged such that at least one pellicle assembly alignment portion 406 and at least one pellicle assembly support pad 408 rests on the gripping portion 412 of each arm 402 a, 402 b. The pellicle assembly gripping portion 400 shown in FIG. 7 includes two pellicle assembly alignment portions 406 and two pellicle assembly support pads 408 on each arm 402 a, 402 b. Each pellicle assembly alignment portion 406 is disposed within a gap 414. Each pellicle assembly support pad 408 is disposed within the gap 414. The surfaces of the generally cubic bodies 416 of the pellicle assembly alignment portions 406 and pellicle assembly support pads 408 may be generally flat. In particular, the surfaces of the pellicle assembly alignment portion 406 and the generally cubic body 416 of the pellicle assembly support pad 408 facing the gap 414 may be generally flat. Each pellicle assembly support pad 408 includes a generally cubic body 416 with a shelf 420. Each shelf 420 protrudes from the corresponding generally cubic body 416. Each shelf 420 protrudes into the gap 414. Each support pad 408 may be described as generally L-shaped. The protruding portion (i.e., shelf 420) of the support pad 408 may be described as providing a ledge. The shelf 420 of the support pad 408 is shaped and arranged to support a portion of the pellicle frame 17. Each shelf 420 is configured to support the ramped portion 49 (see FIG. 3 ) of the pellicle assembly 16. In particular, the ledge 420 of the support pad 408 is shaped and arranged to support the ramped portion 49 of the pellicle frame 17 when the pellicle assembly 16 is placed within the grip portion 412 of the pellicle assembly gripper 400 and when the pellicle assembly gripper 400 is in the closed configuration. The ledge 420 of the support pad 408 is configured to locally contact the surface of the ramped portion 49 of the pellicle assembly 16 and apply a force to this surface generally perpendicular to the plane of the pellicle assembly 16 to support the pellicle assembly 16.

[0160] Each pellicle assembly alignment portion 406 includes a generally cubic body 416 attached to an alignment head 418. Each alignment head 418 protrudes from a portion of the corresponding generally cubic body 416. Each alignment head 418 protrudes into the gap 414. Each alignment head 418 may have a rounded shape. The alignment head 418 of the alignment portion 406 is shaped and positioned to contact a portion of the pellicle frame 17. Each alignment head 418 is configured to contact an edge of the ramped portion 49 (see FIG. 3 ) of the pellicle assembly 16. Specifically, the alignment head 418 of the support pad 408 is shaped and positioned to ensure that the pellicle frame 17 is in a predetermined position when the pellicle assembly 16 is placed within the grip portion 412 of the pellicle assembly gripper 400 and when the pellicle assembly gripper 400 is in the closed configuration. The alignment head 418 of the alignment portion 406 is configured to locally contact the surface of the inclined portion 49 of the pellicle assembly 16 and apply a force to this surface generally within the plane of the pellicle assembly 16 to align the pellicle assembly 16.

[0161] [000160] Pellicle assembly alignment portions 406 and pellicle assembly support pads 408 may be formed from PEEK. Alternatively, pellicle assembly alignment portions 406 and / or pellicle assembly support pads 408 may be formed from a different material.

[0162] The components of the pellicle assembly gripper 400 can be formed according to user requirements. Each of the first arm 402a and the second arm 402b can be formed from a continuous section of material. Each of the first arm 402a and the second arm 402b can be formed from multiple subsections of material. Each of the first arm 402a and the second arm 402b can include one or more cutouts (e.g., voids, openings, or indentations). The cutouts can be beneficial for reducing the weight of the arms 402a, 402b. The cutouts can be beneficial for reducing the manufacturing cost of the arms 402a, 402b. The cutouts can be formed to not include sharp edges. The corners of the cutouts can be rounded. The rounded corners of the cutouts can be beneficial for reducing mechanical stress within the structure in which the cutouts are provided (compared to a structure without the rounded corners). In FIG. 7, the first arm 402a includes a single notch with rounded corners, and the second arm includes two notches with rounded corners.

[0163] [000162] The notch can provide an internal hinge point 419 (e.g., formed as a living hinge). The notch can be shaped to provide an end stop for the movement allowed by the hinge point. The notch can be described as forming an active part of the structure of the pellicle assembly gripper 400. Advantageously, the notch can reduce friction between components (compared to the use of a standard hinge). Reduced friction can reduce particulate generation and subsequent contamination. Additionally, the notch can reduce tolerance build-up (compared to a standard hinge).

[0164] [000163] The patterning device MA (with studs 51) can be transferred to the pellicle frame mounting apparatus 857 without exposure to contaminants. For example, a mask transfer device 881 can be received in a load lock or flow controlled environment within the pellicle frame mounting apparatus 857, and the patterning device MA can be removed from the transfer device in the load lock or flow controlled environment. The patterning device MA can then be transferred to the controlled environment 857 above the partition 862.

[0165] [000164] The patterning device MA can be positioned relative to the pellicle frame mounting arrangement 857 using, for example, a patterning device handling system. The patterning device handling system can comprise a patterning device gripper. Figure 8 shows an example of a patterning device gripper 500. Figure 8A shows a top view of the patterning device gripper 500. Figure 8B shows a perspective view of the patterning device gripper 500. The patterning device gripper 500 comprises a first arm 502a, a second arm 502b, a third arm 502c, a plurality of patterning device alignment portions 506, and a plurality of patterning device support fingers 508.

[0166] [000165] Each of the first arm 502a and the second arm 502b is generally L-shaped. Each of the first arm 502a and the second arm 502b includes a base portion 501 and a distal portion 503. The base portion 501 and the corresponding distal portion 503 are generally perpendicular to each other. The base portion 501 of each of the first arm 502a and the second arm 502b extends from the patterning device gripper control system 522. The base portion 501 of the first arm 502a and the base portion 501 of the second arm 502b are generally perpendicular to each other. The third arm 502c has generally the same shape as the base portion 501 of the second arm 502b. The third arm 502c does not include a distal portion. In the top view of patterning device gripper 500 shown in Figure 8A, third arm 502c is largely hidden from view by second arm 502b. Third arm 502c can be described as being located directly below base 501 of second arm 502b. Because third arm 502c is largely hidden in the views of Figures 8A and 8B, a region 516 is shown in these figures that indicates the spatial extent of the third arm (below second arm 502b).

[0167] The base portion 501 of each of the arms 502a, 502b, 502c is fixed to a patterning device gripper controller 522. The base portion 501 of each of the arms 502a, 502b, 502c is movably attached to the patterning device gripper controller 522. Specifically, the base portion 501 of each of the arms 502a, 502b, 502c is rotatably or pivotally attached to the patterning device gripper controller 522. The points at which each of the arms 502a, 502b, 502c is attached to the patterning device gripper controller 522 are spring loaded. Each of the arms 502a, 502b, and 502c is individually rotatable (relative to the patterning device gripper control system 522) about an axis defined by the point at which each of the arms 502a, 502b, and 502c is movably attached to the patterning device gripper control system 522. Each of the arms 502a, 502b, and 502c can be described as being movable between at least an open position and a closed position. The angle between the base 501 of the arm 502a and the bases 501 of the arms 502b and 502c can be varied by moving the arms 502a, 502b, and 502c. However, when each of the arms 502a, 502b, and 502c is disposed in the closed position, the base 501 of the arm 502a is generally perpendicular to the bases 501 of the arms 502b and 502c. The arms 502a, 502b, 502c are shaped and arranged such that the arms 502a, 502b, 502c define a generally rectangular space 514 therebetween.

[0168] [000167] The size and shape of the generally rectangular space 514 can be varied. The size and shape of the generally rectangular space 514 can be varied by moving the arms 502a, 502b, 502c relative to the patterning device gripper control system 522. The size and shape of the generally rectangular space 514 can be varied using a patterning device gripper control knob 524 that forms part of the patterning device gripper controller 522. The patterning device gripper control knob 524 is configured such that, when rotated, it changes the position and / or rotation of the arms 502a, 502b, 502c (relative to the patterning device gripper control system 522), thereby varying the size and shape of the generally rectangular space 514. The patterning device gripper 500 can be described as being in an open configuration or a closed configuration. The open configuration of the patterning device gripper 500 may correspond to the generally rectangular space 514 defined by the arms 502a, 502b, 502c of the patterning device gripper 500 being larger than the generally rectangular space 514 that exists when the patterning device gripper 500 is in the closed configuration. In Figure 8, the patterning device gripper 500 is shown in the closed configuration. In the closed configuration of the patterning device gripper 500, the dimensions of the generally rectangular space 514 are similar to, but slightly smaller than, the two outer dimensions of the patterning device MA. When the patterning device gripper 500 is in the closed configuration, the spring-loaded connections between each of the arms 502a, 502b, 502c and the patterning device gripper control system 522 allow the generally rectangular space 514 to expand to the size of the two outer dimensions of the patterning device MA. In the open configuration of patterning device gripper 500, generally rectangular space 514 is larger than the space defined by the two outer dimensions of patterning device MA.

[0169] 8 shows a patterning device gripper 500 with one patterning device support finger 508 attached to the base 501 of a first arm 502a, one patterning device support finger 508 attached to the distal end 503 of the first arm 502a, and one patterning device support finger 508 attached to the base 501 of a second arm 502b.

[0170] [000169] The protrusions 510 of the patterning device support fingers 508 can be described as providing protrusions. The protrusions 510 of the patterning device support fingers 508 are shaped and arranged to support portions of the patterning device MA. In particular, the protrusions 510 of the support fingers 508 are shaped and arranged to support portions of the patterning device MA when the patterning device MA16 is positioned within the generally rectangular space 514 and when the patterning device gripper 500 is in the closed configuration. The protrusions 510 of the patterning device support fingers 508 are configured to locally contact a surface of the patterning device and apply a force to this surface generally perpendicular to the plane of the patterning device to support the patterning device.

[0171] Each patterning device alignment portion 506 includes a generally cylindrical member. The generally cylindrical member can be described as a wheel. Each patterning device alignment portion 506 is attached to one of the arms 502 a, 502 b, 502 c using an axle and one or more complementary members such that the patterning device alignment portion 506 is rotatable about a longitudinal axis. Each patterning device alignment portion 506 protrudes from one of the arms 502 a, 502 b, 502 c into a generally rectangular space 514. 8 shows a patterning device gripper 500 with one patterning device alignment feature 506 attached to the base 501 of the first arm 502a, one patterning device alignment feature 506 attached to the distal portion 503 of the first arm 502a, one patterning device alignment feature 506 attached to the third arm 502c, and two patterning device alignment features 506 attached to the distal portion 503 of the second arm 502b. The patterning device alignment features 506 are shaped and positioned to contact portions of the patterning device MA. Specifically, the patterning device alignment features 506 are shaped and positioned to ensure that the patterning device MA is in a predetermined position when the patterning device MA is placed within the generally rectangular space 514 and when the patterning device gripper 500 is in the closed configuration. The patterning device alignment portion 506 is configured to locally contact a surface of the patterning device MA and apply a force to this surface generally in the plane of the patterning device MA to align the patterning device MA.

[0172] [000171] Patterning device alignment features 506 and patterning device support fingers 508 may be formed from PEEK. Alternatively, patterning device alignment features 506 and / or patterning device support fingers 508 may be formed from a different material.

[0173] [000172] The components of the patterning device gripper 500 can be formed according to user requirements. Each of the arms 502a, 502b, 502c can be formed from a continuous section of material. Each of the arms 502a, 502b, 502c can be formed from multiple subsections of material. Each of the arms 502a, 502b, 502c can include one or more cutouts (e.g., voids, openings, or depressions). The cutouts can be beneficial for reducing the weight of the arms 502a, 502b, 502c. The cutouts can be beneficial for reducing the manufacturing cost of the arms 502a, 502b, 502c. The cutouts can be formed to be free of sharp edges. The corners of the cutouts can be rounded. The rounded corners of the cutouts can be beneficial for reducing mechanical stress within the structure in which the cutouts are provided (compared to when the rounded corners are not provided). In FIG. 8, each of arms 502a, 502b, 502c of patterning device gripper 500 includes a number of notches with rounded corners.

[0174] [000173] The notch can provide an internal hinge point (e.g., formed as a living hinge). The notch can be shaped to provide an end stop for the movement allowed by the hinge point. The notch can be described as forming an active part of the structure of the patterning device gripper 500. Advantageously, the notch can reduce friction between components (compared to the use of standard hinges). Reduced friction can reduce particle generation and subsequent contamination. Furthermore, the notch can reduce tolerance buildup (compared to standard hinges).

[0175] [000174] Figure 9A shows an exemplary mechanism 200 comprising the pellicle assembly gripper 400 shown in Figures 7A and 7B and the patterning device gripper 500 shown in Figures 8A and 8B.

[0176] 9A , first arm 402a, second arm 402b, and pellicle assembly gripper control system 422 are attached to a first intermediate member 426. First intermediate member 426 includes a handle 428, a vertical control knob 430, and a locking block 432. Similarly, patterning device gripper control system 522 is attached to a second intermediate member 526. Second intermediate member 526 includes a handle 528, a vertical control knob 530, and a locking block 532. First intermediate member 426 is attached to damper assembly 201. Second intermediate member 526 is attached to damper assembly 202.

[0177] 9B illustrates the damper assembly 202 in more detail. The damper assembly 202 includes a body 210 having a cavity 212 and a damper mechanism 214 disposed within the cavity 212. The damper mechanism 214 includes a piston housing 204, a piston 206, and a fastener 208. The piston 206 is movable relative to the piston housing 204. The piston 206 is movable relative to the piston housing 204 in generally only one dimension. This dimension may be the z-dimension (see axes in FIGS. 9A and 9B). The piston 206 is movably attached to the end of the piston housing 204, allowing it to vary its extent of containment within the piston housing 204. The piston 206 remains generally stationary unless acted upon by an external force. The function of the piston 206 is to damp movement. Damping may be achieved using a hydraulic damping mechanism within the piston housing 204. The damper mechanism 214 can damp the movement of the piston 206 (relative to the piston housing 204) in one dimension in which the piston 206 can move. The fastener 208 is secured to an end of the piston 206 opposite the end of the piston 206 proximate the piston housing 204.

[0178] 9A , a second intermediate member 526 supports the patterning device gripper 500, and the second intermediate member 526 is fixed to the fastening means 208. A vertical control knob 530 is operable to raise or lower a portion of the patterning device gripper 500. This may be useful for positioning the patterning device MA using the patterning device gripper 500. The vertical control knob 530 may be operated manually. Movement of the patterning device gripper 500 in the vertical direction (z-direction in FIG. 9 ) may be damped by the damper assembly 202. Specifically, the vertical movement of the patterning device gripper 500 caused by use of the vertical control knob 530 may be damped by the damper assembly 202. In addition to fastening the second intermediate member 526 to the fastening means 208, the second intermediate member 526 may be attached to the damper assembly 202 by other means while still allowing the damper mechanism 214 to damp the movement of the patterning device gripping portion 500.

[0179] It will be appreciated that first intermediate member 426 and damper assembly 201 may include substantially the same components as second intermediate member 526 and damper assembly 202, respectively. It will also be appreciated that first intermediate member 426 and damper assembly 201 may provide substantially the same functionality as second intermediate member 526 and damper assembly 202, respectively. Specifically, vertical movement of pellicle assembly gripper 400 may be effected by vertical control knob 430, and vertical movement of pellicle assembly gripper 400 may be damped by damper assembly 201.

[0180] [000179] Damper assembly 201 and damper assembly 202 are each movably mounted on rails 218. A second intermediate member 526 supports patterning device gripper 500 and is attached to fastening means 208 of damper assembly 202. A first intermediate member 426 supports pellicle assembly gripper 400 and is attached to fastening means of damper assembly 201 that are identical to fastening means 208 of damper assembly 202.

[0181] 9C illustrates the lock block 432 in greater detail. The lock block 432 includes a housing 222, a pin 224, a pin handle 226, a wheel 228, and a plurality of fastening bolts 230. The housing 222 of the lock block 432 is fixed to the first intermediate member 426 and the damper assembly 201 using a plurality of fastening bolts. The pin 224 is disposed within the housing 222 and protrudes from both sides of the housing 222. The pin handle 226 is attached to one end of the pin 224. The wheel 228 is disposed on the end of the pin 224 opposite the pin handle 226, so that the pin 224 protrudes from a central opening in the wheel 228. The wheel 228 and the pin 224 share a common longitudinal axis. The wheel 228 is attached to the housing 222 so as to be operable to rotate about the common longitudinal axis of the wheel 228 and the pin 224. The wheel 228 can be attached to the housing 222 using a mechanism including a ball bearing. A separate ball bearing mechanism can be provided between the pin 224 and the wheel 228. The pin 224 is operable to move in a direction parallel to a common longitudinal axis of the wheel 228 and the pin 224. A mechanism (such as a spring mechanism) housed within the housing 222 biases the pin 224 to an equilibrium position in which the pin 224 protrudes a predetermined amount from the surface of the housing 222. The pin handle 226 can be operated to move the pin 224 in a direction parallel to the common longitudinal axis of the wheel 228 and the pin 224. Specifically, manually pulling the pin handle 226 moves the pin 224 in a direction toward the pin handle 226. When the pin handle 226 is not operated, the mechanism (such as a spring mechanism) housed within the housing 222 returns the pin 224 to its equilibrium position.

[0182] 9D shows rail 218 with tracks 232, 234 highlighted. Wheel 228 of locking block 432 is sized to fit within first track 232 disposed within rail 218. First track 232 defines a path that is generally a straight line parallel to the x-direction (see axis in FIG. 9D ). Handle 428 (see FIG. 9A ) can be used to manually move pellicle assembly gripper 400 along first track 232 of rail 218. Locking block 432 can be used to lock and unlock the position of pellicle assembly gripper 400 relative to first track 232 of rail 218. When locking block 432 is not actuated, pin 224 protrudes from housing 222 and engages rail 218, thereby fixing the position of pellicle assembly gripper 400 along the path defined by first track 232. When the pin handle 226 is pulled, the pin 224 retracts at least partially into the housing 222 and no longer engages with the rail 218, allowing the handle 428 to be used to move the pellicle assembly gripper 400 along the path defined by the first track 232.

[0183] [000182] Lock block 532 is equivalent to lock block 432. In a configuration equivalent to lock block 432, first intermediate member 426, and damper assembly 201 described above, a housing of lock block 532 is secured to second intermediate member 526 and damper assembly 202 using a plurality of fastening bolts. The wheels of lock block 532 are sized to fit within second track 234 disposed within rail 218 shown in FIG. 9D. The path defined by second track 234 is partially straight and generally parallel to the x-direction, and partially has a component in the z-direction (see FIG. 9D), such that second track 234 is partially disposed below first track 232. A handle 528 (see FIG. 9A) can be used to manually move patterning device gripper 500 along second track 234 of rail 218. Locking block 532 , similar to locking block 432 described above, provides a mechanism for locking and unlocking the position of patterning device gripper 500 relative to second track 234 of rail 218 .

[0184] The locking blocks 432, 532 are operable to lock the position of the grippers 400, 500. This can be useful when the grippers 400, 500 are used to present the pellicle assembly 16 and patterning device MA to the intermediate support structure 98 of the pellicle frame mounting apparatus 857 (see FIG. 6 ), as will be described in more detail below. Furthermore, moving the pellicle assembly gripper 400 along the first track 232 or the patterning device gripper 500 along the second track 234 typically requires the use of two hands (one hand holding the handles 428, 528 and the other operating the pin handle 226). This prevents accidental operation of the vertical control knobs 430, 530 while the grippers 400, 500 are moving relative to the tracks 232, 234. This can be described as a safety mechanism.

[0185] [000184] The pellicle assembly gripper 400 is operable to grip the pellicle assembly 16. The pellicle assembly gripper 400 and / or the pellicle assembly 16 can be manipulated so that the first arm 402a and the second arm 402b surround the pellicle assembly 16 when the pellicle assembly gripper 400 is in an open configuration. The arms 402a, 402b of the pellicle assembly gripper 400 can then be moved using the pellicle assembly gripper control knob 424 so that the pellicle assembly gripper 400 is in a closed configuration. This action grips the pellicle assembly 16. A plurality of pellicle assembly alignment features 406 ensure that the pellicle assembly 16 is in the desired position. A plurality of pellicle assembly support pads 408 support the pellicle assembly 16. Specifically, pellicle assembly 16 is presented to pellicle assembly gripper 400 such that protrusions 420 of support pads 408 are positioned to contact the side of pellicle frame 17 that faces away from patterning device MA. Pellicle assembly alignment features 406 and pellicle assembly support pads 408 directly contact pellicle frame 17 of pellicle assembly 16 (and no other components contact it). Thus, pellicle assembly gripper 400 is used to contact only a very small portion of the periphery of pellicle frame 17. Advantageously, this reduces the risk of particle contamination of pellicle frame 16 compared to grippers that contact a larger portion of the periphery of pellicle frame 17.

[0186] [000185] Pellicle assembly gripper 400 and control system 870 (see FIG. 6) may form part of pellicle frame mounting apparatus 857. Pellicle assembly gripper 400 (which grips pellicle assembly 16) and / or control system 870 may be manipulated to position pellicle assembly 16 above partition 862 of pellicle frame mounting apparatus 857. Pellicle assembly gripper 400 may then be switched to an open configuration using pellicle assembly gripper control knob 424, causing pellicle assembly gripper 400 to release pellicle assembly 16 onto intermediate support structure 98 (see FIG. 6).

[0187] [000186] The patterning device gripper 500 is operable to grip a patterning device MA. The patterning device gripper 500 and / or the patterning device MA can be manipulated so that the arms 502a, 502b, 502c surround the patterning device MA when the patterning device gripper 500 is in an open configuration. The arms 502a, 502b, 502c can then be moved using the patterning device gripper control knob 524 so that the patterning device gripper 500 is in a closed configuration. This action grips the patterning device MA. A plurality of patterning device alignment features 506 ensure that the patterning device MA is in a desired position. A plurality of patterning device support fingers 508 support the patterning device MA. The patterning device alignment features 506 and the patterning device support fingers 508 directly contact the patterning device MA (and no other components contact it). Thus, only a small portion of the patterning device MA is contacted with patterning device gripper 500. Advantageously, this reduces the risk of particle contamination of the patterning device MA compared to grippers that contact a larger portion of the patterning device MA.

[0188] [000187] Patterning device gripper 500 and control system 870 (see FIG. 6 ) may form part of pellicle frame mounting apparatus 857. Patterning device gripper 500 (which grips patterning device MA) and / or control system 870 may be manipulated to place the patterning device MA in a position above partition 862 of pellicle frame mounting apparatus 857. Patterning device gripper 500 may then release the patterning device MA onto intermediate support structure 98 of pellicle frame mounting apparatus 857 such that the patterning device MA is positioned above pellicle assembly 16, which is already positioned on intermediate support structure 98, as described above. Patterning device gripper 500 may be released by switching patterning device gripper 500 to an open configuration using patterning device gripper control knob 524.

[0189] [000188] For example, the patterning device MA may be damaged if it is dropped. For example, the patterning device MA may be damaged if it falls into the generally rectangular space 514 of the patterning device holder 500. Because the second intermediate member 526 is attached to the rails 218 via the damper assembly 202, the movement of the patterning device holder 500 parallel to the z-axis is damped. The damper assembly 202 can therefore reduce the impact force of the patterning device MA falling into the generally rectangular space 514 of the patterning device holder 500. Advantageously, this can reduce damage to the patterning device MA.

[0190] [000189] Manipulating the pellicle assembly gripper 400 as described above may include moving the pellicle assembly gripper 400 relative to the first track 232 of the rail 218. This may be done manually. The handle 428 may be used to manually move the pellicle assembly gripper 400. Manipulating the patterning device gripper 500 as described above may include moving the patterning device gripper 500 relative to the second track 234 of the rail 218. This may be done manually. The handle 528 may be used to manually move the patterning device gripper 500. The rail 218 may form part of the pellicle frame mounting arrangement 857.

[0191] 9A , one or both of first intermediate member 426 and second intermediate member 526 may be movably mounted directly to rail 218 (i.e., without damper assemblies 201, 202). As another alternative, pellicle assembly gripper 400 and patterning device gripper 500 may be movably mounted to separate rails (with or without damper assemblies 201, 202). Moveably mounting pellicle assembly gripper 400 and patterning device gripper 500 to a common rail 218 (as shown in mechanism 200 of FIG. 9A ) may allow for more accurate relative positioning of pellicle assembly 16 and patterning device MA.

[0192] [000191] Pellicle assembly gripper 400 and patterning device gripper 500 have been described above in the context of pellicle frame mounting apparatus 857. It will be appreciated that pellicle assembly gripper 400 and patterning device gripper 500 are operable to manipulate pellicle assembly 16 and patterning device MA, respectively, for other applications. For example, pellicle assembly gripper 400 can be used to handle pellicle assembly 16 within pellicle mounting apparatus 855 (see FIG. 2). As another example, patterning device gripper 500 can be used to handle patterning device MA within stud mounting apparatus 840 (see FIG. 2). The advantages of pellicle assembly gripper 400 and patterning device gripper 500 described above generally apply to other uses of pellicle assembly gripper 400 and patterning device gripper 500.

[0193] 6, the pellicle frame mounting device 857 includes an actuator 111. The actuator 111 can be used to adjust the position of the pellicle assembly 16 in the x, y, and z directions, as well as to rotate the pellicle assembly about the z direction.

[0194] [000193] Partition 862 is provided with four windows 893, 894. Windows 893, 894 may be formed, for example, from quartz. Two of the windows 893 are positioned to allow imaging sensors 106 to view alignment marks provided on patterning device MA. Note that only one of the two windows 893 and only one of the two imaging sensors 106 are visible in Figure 6. The other two windows 894 are positioned to allow imaging sensors 105 to view pellicle frame 17 (e.g., view the corners of the pellicle frame).

[0195] [000194] Figure 10 shows in more detail an arrangement 600 for measuring the position of pellicle assembly 16 using imaging sensor 105. The arrangement 600 of the apparatus shown in Figure 10 may form part of pellicle frame mounting apparatus 857 shown in Figure 6. The arrangement 600 of the apparatus shown in Figure 10 shows components not shown in Figure 6. These components may form part of pellicle frame mounting apparatus 857, but are not shown in Figure 6 for clarity. Note that the apparatus of Figure 10 has a perpendicular orientation relative to the apparatus of Figure 6.

[0196] [000195] The arrangement 600 includes an imaging sensor 105, a radiation source 602, a beam splitter 604, a quarter wave plate 606, a window 894 with alignment marks 109, a protective window 607, a pellicle 19 with a pellicle frame 17, and a patterning device MA. The imaging sensor 105 includes an array of sensor elements and may be, for example, a camera. The radiation source 602 may be a light emitting diode (LED). The windows 894, 607 may be generally transparent. The protective window 607 may protect the alignment marks 109 from particle contamination or other debris.

[0197] 10, the imaging sensor 105, window 894, protective window 607, pellicle 19, and patterning device MA are arranged in a similar manner as shown in FIG. 6. The beam splitter 604 is located between the imaging sensor 105 and the window 894. The quarter-wave plate 606 is located between the beam splitter 604 and the window 894. The imaging sensor 105, the beam splitter 604, the quarter-wave plate 606, the window 894, and the protective window 607 can be described as being aligned such that they are all on an axis 618 and are spaced apart in the direction of the axis 618. This axis 618 is the z-axis. The radiation source 602 is located proximate to the beam splitter 604. The radiation source 602 is located such that the radiation source 602 and the beam splitter 604 are separated in a direction 608 perpendicular to the axis (such as the y-axis).

[0198] [000197] The mechanism 600 may be referred to as an optical measurement system. The optical measurement system illustrated in Figure 10 is operable to measure the position of the pellicle frame 17 relative to the alignment marks 109. The optical measurement system may provide measurements of the position of the pellicle frame 17 with an accuracy of 5 μm or better. The optical measurement system may be based on a telecentric optical system.

[0199] [000198] In use, the radiation source 602 emits an unpolarized beam 608 in a direction perpendicular to the axis 618. The unpolarized beam 608 is incident on the beam splitter 604. The beam splitter 604 splits the unpolarized beam 608 into two linearly polarized beams 610, 612 propagating in mutually perpendicular directions. The first beam 610 is p-polarized, i.e., the first beam 610 is linearly polarized and the polarization direction is perpendicular to the plane of incidence (i.e., out-of-plane in Figure 10). The first beam 610 propagates in the same direction as the unpolarized beam 608 emitted by the radiation source 602. The second beam 612 is s-polarized, i.e., the second beam 612 is linearly polarized and the polarization direction is parallel to the plane of incidence (i.e., in-plane in Figure 10). The second beam 612 propagates parallel to the axis 618 towards the quarter-wave plate 606.

[0200] [000199] Quarter-wave plate 606 is positioned such that the axis of quarter-wave plate 606 is aligned at 45 degrees to the direction of linear polarization of second beam 612. After propagating through quarter-wave plate 606, second beam 612 becomes circularly polarized beam 614. Circularly polarized beam 614 may be at least partially transmitted through window 894, protective window 607, pellicle 19, and / or pellicle frame 17. Circularly polarized beam 614 may be at least partially reflected from alignment mark 109, pellicle 19, pellicle frame 17, and / or patterning device MA. Reflected circularly polarized beam 614 becomes reflected circularly polarized beam 616, which has a circular polarization opposite to the direction of circular polarization of circularly polarized beam 614. Reflected circularly polarized beam 616 propagates toward quarter-wave plate 606.

[0201] [000200] After propagating through quarter-wave plate 606, reflected circularly polarized beam 616 becomes linearly polarized beam 618. The direction of linear polarization of linearly polarized beam 618 is rotated 90 degrees relative to the direction of linear polarization of second beam 612. Specifically, second beam 612 is s-polarized (has a polarization direction in the plane of FIG. 10 ), and linearly polarized beam 618 is p-polarized (has a polarization direction out of the plane of FIG. 10 ). Linearly polarized beam 618 propagates through beam splitter 604. As a result of the p-polarization of linearly polarized beam 618, linearly polarized beam 618 is not split by beam splitter 604. Linearly polarized beam 618 transmits through beam splitter 604 as transmitted beam 620. Transmitted beam 620 then enters imaging sensor 105.

[0202] [000201] Pellicle 19 can be more transmissive to radiation from circularly polarized beam 614 than pellicle frame 17 (which can block substantially all of this radiation). At least a portion of circularly polarized beam 614 is incident on and reflected by patterning device MA. The edges of pellicle frame 17 can block the light reflected from patterning device MA. At least a portion of the radiation reflected from patterning device MA is incident on imaging sensor 105 (as transmitted beam 620), where it can have a measured spatial intensity (e.g., a measured image) that varies depending on the position of the edge of pellicle frame 17. In particular, the difference in light transmission levels between pellicle 19 and pellicle frame 17 can provide spatial contrast in the intensity measurement. This spatial contrast can be particularly useful in measuring the position of pellicle assembly 16 and subsequently aligning pellicle assembly 16. For example, the position of the pellicle assembly 16 can be measured relative to an alignment mark 109 imaged by the imaging sensor 105 .

[0203] [000202] Quarter-wave plate 606 performs a phase shift (between two orthogonal components of the electric field intensity) on light reflected from patterning device MA (such as reflected circularly polarized beam 616) as it propagates through quarter-wave plate 606. This phase shift is performed so that the light reflected from patterning device MA is maximally transmitted through beam splitter 604. Maximum transmission of light through beam splitter 604 results in a high signal in the intensity measurement performed by imaging sensor 105. For example, measurements performed by imaging sensor 105 are subject to background light, which can reduce the contrast of images representing the edges of pellicle 19 and pellicle frame 17. However, because such background radiation is unpolarized, only a portion (e.g., half) of such background radiation may reach the imaging sensor. In contrast, signal radiation (i.e., the portion of transmitted beam 620 reflected from patterning device MA) is maximally transmitted through beam splitter 604. 10 allows maximum transmission of this signal light through beam splitter 604, thereby providing high spatial contrast in measurements performed by the imaging sensor, thereby enabling the position of pellicle assembly 16 to be measured with high precision.

[0204] [000203] Figure 11 shows in more detail an arrangement 700 for measuring the position of the patterning device MA using imaging sensor 106. The arrangement 700 of the apparatus shown in Figure 11 may form part of the pellicle frame mounting arrangement 857 shown in Figure 6. The arrangement 700 of the apparatus shown in Figure 11 shows components that are not shown in Figure 6. These components may form part of the pellicle frame mounting arrangement 857, but are not shown in Figure 6 for clarity. Note that the apparatus of Figure 11 has a perpendicular orientation to the apparatus of Figure 6.

[0205] [000204] Arrangement 700 comprises imaging sensor 106, radiation source 702, window 893 containing alignment marks 109, and patterning device MA containing alignment marks 704. Imaging sensor 106 comprises an array of sensor elements and may be, for example, a camera. Radiation source 702 may be an LED. Alignment marks 109 are arranged on window 893 to form a diffraction grating. Alignment marks 704 are arranged on patterning device MA to form a diffraction grating.

[0206] [000205] In Figure 11, imaging sensor 106, window 893 and patterning device MA are positioned in a similar manner as shown in Figure 6. Radiation source 702 is positioned so as not to block the optical path between imaging sensor 106 and window 893. Radiation source 702 may be positioned close to imaging sensor 106.

[0207] [000206] The arrangement 700 may be referred to as an optical measurement system. The optical measurement system illustrated in Figure 11 is operable to measure the position of the patterning device MA relative to the alignment marks 109.

[0208] [000207] In use, the radiation source 702 emits a light beam 706. The beam 706 propagates towards the window 893. A portion of the beam 706 may be backscattered (e.g. reflected) from the alignment mark 109. Another portion of the beam 706 may be transmitted through the window 893 and then backscattered (e.g. reflected) from the alignment mark 704. Because the alignment marks 109, 704 are arranged to form a reflective diffraction grating, the portion of the beam 704 that is backscattered from the alignment marks 109, 704 forms multiple diffraction orders. Figure 11 shows a beam 708 that corresponds to a zero-order reflection of the beam 706 from the alignment mark 109 located on the window 893 and from the alignment mark 704 located on the patterning device MA. 11 also shows beam 710, which corresponds to the first order (reflective) diffraction of beam 706 from alignment mark 109 located on window 893 and from alignment mark 704 located on patterning device MA. First order beam 710 is incident on imaging sensor 106, which is therefore operable to measure a signal corresponding to the position of patterning device MA. Zero order beam 708 (corresponding to standard reflection) is not incident on imaging sensor 106.

[0209] [000208] The angle at which the beam 706 is backscattered from the alignment marks 109, 704 depends on the angle of incidence between the beam 706 and the alignment marks 109, 704. This angle also depends on the wavelength of the beam 706. This angle also varies with the pitch of the alignment marks 109, 704. In the arrangement 700 shown in Figure 11, the angle of incidence, the wavelength of the light, and the pitch of the alignment marks 109, 704 may be selected so that the primary beam 710 is normal to the plane of the patterning device MA. Similarly, the primary beam may be configured to be normal to the plane of the pellicle 19.

[0210] [000209] It may be desirable to measure the position of the patterning device MA in stud mounting arrangement 840 and / or pellicle frame mounting arrangement 857 (see, for example, FIG. 2). It may also be desirable to measure the position of the patterning device MA when the patterning device MA is used in other contexts (e.g., in lithographic apparatus LA). Alignment marks 704 may be provided on the patterning device MA to allow the position of the patterning device MA to be measured when the patterning device MA is used in other contexts (e.g., in lithographic apparatus LA).

[0211] 11 is operable to measure the position of alignment mark 109 (fixed relative to pellicle frame mounting apparatus 857) and alignment mark 704 (fixed relative to patterning device MA). Accordingly, mechanism 700 shown in FIG. 11 is operable to measure the position of patterning device MA relative to pellicle frame mounting apparatus 857. This can be used to align patterning device MA relative to pellicle frame mounting apparatus 857. Advantageously, the measurement of the positions of alignment mark 109 and alignment mark 704 is based on measuring the diffraction orders of light (as described above) and is performed using the same measurement apparatus (mechanism 700). This results in an accurate measurement of the position of the patterning device MA. This allows for a more accurate measurement of the position of the patterning device MA than would be possible if the position of the patterning device MA were based on measuring the edge position of the patterning device MA.

[0212] [000211] Mechanisms 600, 700 have been described in the context of pellicle frame mounting apparatus 857. It will be appreciated that mechanisms 600, 700 may be used in other applications. For example, mechanism 600 may be used to measure the position of pellicle assembly 16 in pellicle mounting apparatus 855 (see FIG. 2). As another example, mechanism 700 may be used to measure the position of patterning device MA in stud mounting apparatus 840 (see FIG. 2). The advantages of mechanisms 600, 700 described above generally apply when mechanisms 600, 700 are used in other applications.

[0213] [000212] The alignment marks 109, 704 may be provided with stickers. The stickers may be formed from anodized aluminum. The stickers may be black. The stickers may have a generally circular shape. The stickers may include apertures. The stickers may increase the effective size of the alignment marks 109, 704. The stickers may reduce interference between light reflected from the alignment marks 109, 704 and other light. The provision of stickers may increase the contrast of images acquired using the imaging sensors 105, 106. In particular, the provision of stickers may increase the visibility of the alignment marks 109, 704 against background light. The provision of stickers may limit the dispersion of light reflected from the alignment marks 109, 704. Therefore, the alignment marks 109, 704 may appear sharper when measured by the imaging sensors 105, 106. This may increase the accuracy of position measurements based on measuring the positions of the alignment marks 109, 704.

[0214] [000213] The advantages of providing stickers may be beneficial when measuring the position of the pellicle assembly 16 using the arrangement 600 shown in Figure 12 and / or when measuring the position of the patterning device MA using the arrangement 700 shown in Figure 13. Alternatively, the alignment marks 109, 704 may be provided with a coating that achieves the same benefits as the stickers.

[0215] [000214] The imaging sensors 105, 106 shown in Figures 10 and 11 may correspond to the imaging sensors 105, 106 shown in Figure 6 .

[0216] [000215] The alignment of the two elements using alignment marks is well known in the art and will not be described further here. The actuator 111 and mechanisms 600, 700 can be collectively referred to as the control system 870.

[0217] 12 shows partition 862 in more detail. A gas outlet (not shown) can be configured to supply gas to the side of partition 862 visible in FIG. 12. The gas can be delivered at a higher pressure than the gas pressure on the opposite side of partition 862. Partition 862 also includes holes 895 positioned to coincide with the positions of engagement mechanisms 50 of pellicle assembly 16. One of the holes 895 is shown in more detail in FIG. 13. Hole 895 is sized to allow pin 1090 and operating pin 1092 to protrude through the hole. Hooks 1091 protrude from both sides of the hole. In other words, hooks 1091 are fixed to partition 862 and protrude from the partition. Pin 1090, hooks 1091, and operating pin 1092 are also shown in FIGS. 6, 12, and 14.

[0218] [000217] As mentioned above, the controlled environment 859 above the partition 862 can be maintained at a higher pressure than the pressure below the partition (e.g., by pumping gas above the partition). As can be seen in FIG. 12, the opening 895 in the partition 862 is relatively small, limiting the possibility of contamination entering the controlled environment through this opening. This possibility is further reduced by the higher pressure in the controlled environment 859 compared to the environment in the feed partition 862. This higher pressure ensures that air flows downward through the opening 895, carrying contamination away from the pellicle 19.

[0219] [000218] When pellicle assembly 16 is fixed to patterning device MA, imaging sensors 105, 106 are used to monitor the position of pellicle assembly 16 relative to patterning device MA. This is done after pellicle assembly 16 is lifted from intermediate support structure 98 by pins 1090. The position of pellicle assembly 16 is adjusted using actuator 111, which moves support structure 101 and therefore pellicle assembly 16 relative to patterning device MA. Operation of actuator 111 can be manual or controlled by an automated controller. Movement of support structure 101 can continue until pellicle assembly 16 is aligned with patterning device MA.

[0220] [000219] Once the pellicle assembly 16 is correctly positioned relative to the patterning device MA, pins 1090, hooks 1091 and actuation pins 1092 are used to engage engagement features 50 with studs 51 protruding from the patterning device MA.

[0221] FIG. 14 schematically illustrates how the pin 1090, the hook-shaped member 1091, and the operating portion 1092 can move relative to one another. As described above, the hook-shaped member 1091 extends from the support structure 101 and therefore cannot move relative to the support structure. The support structure 101 itself, as described above, can move, including in the generally vertical direction (z direction). The operating pin 1092 can be moved in the generally vertical direction (z direction) by the actuator 320. Both operating pins 1092 are fixed to the actuator 320, so they move together. The pin 1090, which supports the pellicle frame 17, is not actively movable relative to the operating pin 1092. The pin 1090 is connected to the actuator 320 via a spring 322. Therefore, upward and downward movement of the actuator 320 causes a corresponding movement of the pin 1090, except when the pin is in contact with the pellicle frame 17. If pin 1090 is in contact with pellicle frame 17, further upward movement of actuator 320 will not cause further upward movement of the pin, resulting in compression of spring 322. Once spring 322 is compressed, downward movement of actuator 320 will not cause downward movement of pin 1090 until spring 322 stretches to its relaxed configuration.

[0222] [000221] Each actuation pin 1092 includes a curved surface (e.g., a generally convex curved surface) at the end of a generally cylindrical body. The curved end of actuation pin 1092 contacts a portion of engagement mechanism 50 when pin 1090, hook 1091, and actuation pin 1092 are used to engage engagement mechanism 50 with stud 51 protruding from patterning device MA. This process is further described below with reference to Figure 17D. The curved surface is shaped to minimize slippage between actuation pin 1092 and the portion of engagement mechanism 50.

[0223] 15 and 16 show a schematic of how the engagement mechanism 50 engages the protrusion 51 (which may also be referred to as a stud). FIGS. 15 and 16 show a cross-sectional view from one side and a bottom view of the engagement mechanism 50 and the protrusion 51. Referring first to FIG. 15, the engagement arm 80 is pushed away from the cap 66 using an actuation pin 1092 (not shown) that pushes against the distal end of the engagement arm 80. As can be seen in FIG. 15, the engagement mechanism 50 and the protrusion 51 are not in contact at this point.

[0224] [000223] The engagement features are moved in the x direction until the distal heads 53 of the projections 51 are positioned above the engagement tabs 81 projecting from the engagement arms 80. This movement is achieved by moving the pellicle frame 17 to which the engagement features 50 are fixed, thus moving all of the engagement features 50 in unison.

[0225] [000224] Once the engagement mechanism 50 is in place, the actuation pin that has been pushing the engagement arm 80 away from the distal head 53 of the projection 51 is released. Because the engagement arm 80 is resilient, it moves downward and presses against the inner surface of the distal head 53. Thus, the engagement tab 81 presses the distal head 53 against the cap 66, thereby securing the engagement mechanism 50 to the projection 51. This is shown in FIG. 16.

[0226] [000225] It may be desirable to remove the pellicle assembly 16 from the patterning device MA (for example, if contamination is detected on the pellicle). This can be done by the pellicle frame attachment apparatus 857. To disengage the engagement mechanism 50 from the protrusions 51, the above sequence is reversed.

[0227] [000226] The operation of the pin 1090, hook 1091 and operating pin 1092 can be manual, automatic or semi-automatic.

[0228] [000227] The pin 1090, hook 1091, and actuation pin 1092 may be formed from, for example, steel. The surfaces of the pin 1090, hook 1091, and actuation pin 1092 that contact the engagement mechanism 50 may be provided with a coating of a material such as PEEK or some other robust material. Alternatively, the contact surfaces may simply be polished surfaces of the pin 1090, hook 1091, and actuation pin 1092.

[0229] [000228] Once the pellicle assembly 16 and patterning device MA are connected to form the mask assembly 15, the mask assembly can be placed in a mask assembly transport device 853 for transport to the lithographic apparatus LA (see Figure 2).

[0230] 17A through 17H show in more detail one way in which engagement feature 50 can engage protrusion 51. Referring first to FIG. 17A , pin 1090 is moved in the z direction until it contacts cap 66 of engagement feature 50. Pin 1090 is further moved in the z direction to lift engagement feature 50. Because the engagement feature is fixed to frame 17 (see FIG. 3 ), this lifts the entire pellicle assembly 16. Pin 1090 is one of four pins 1090 (see FIG. 12 ), which move in unison. Thus, pellicle assembly 16 is lifted by and supported by the four pins 1090. Actuator 111 (see FIG. 6 ) is then used to adjust the position of pellicle assembly 16 until the pellicle assembly is aligned with patterning device MA.

[0231] 17B, ​​the two hook-shaped members are then moved in the z direction until their distal ends are above the top surface of the first support arm 82a. Then, the hook-shaped members 1091 are moved in the x direction until their distal ends are above the corner plate 1089 of the support arm 82a.

[0232] 17C, the hook 1091 is then moved downward until it contacts the corner plate 1089 of the support arm 82a. The pin 1090 and hook 1091 together grip the engagement mechanism 50, allowing subsequent operation of the engagement mechanism.

[0233] 17D , the operating pin 1092 is moved in a generally vertical direction to push the block 54 provided at the distal end of the engagement arm 80. The operating pin 1092 pushes the engagement arm 80 upward, thereby expanding the space between the engagement tab 81 and the cap 66. As described above, the surface of each operating pin 1092 that contacts the distal end of the engagement arm 80 (particularly, the block 54 provided at the distal end of the engagement arm 80) is curved. The curved surface can be a generally convex curved surface. The curved surface of the operating pin 1092 is shaped so that, when the operating pin 1092 pushes the engagement arm 80 upward, the contact edge between the operating pin 1092 and the distal end of the engagement arm 80 shifts smoothly along the curved surface. This minimizes the contact surface area between the operating pin 1092 and the block 54 provided at the distal end of the engagement arm 80. Advantageously, such a design of the actuation pin 1092 can ensure minimal slippage between the actuation pin 1092 and the block 54 provided at the distal end of the engagement arm 80. In Figure 17D, the engagement arm 80 is not bent upwards due to limitations in the software used to generate the drawing.

[0234] 17E and 17F, the engagement mechanism 50 is then moved in the x direction until the distal end 53 of the projection 51 is positioned above the cap 66 and below the engagement tab 81.

[0235] [000234] As noted above, all of the engagement features 50A-50D move in unison via movement of pin 1090. In an alternative mechanism, the patterning device MA and protrusions 51 can all move without moving the pellicle frame 17. Generally, only lateral relative movement between the protrusions and the engagement features is required. The direction of lateral movement depends on the orientation of the engagement arms 80 (e.g., it may be in the y direction instead of the x direction).

[0236] 17F, once the cap 66 is positioned under the distal head 53 and the engagement tab 81 is above the distal head 53, the actuation pin 1092 is retracted. The resilience of the engagement arm 80 causes it to return towards its initial position, thus pressing the engagement tab 81 against the distal head 53. The engagement tab 81 presses the distal head 53 against the cap 66, thereby securing the engagement mechanism 50 relative to the projection 51.

[0237] 17G, the hook 1091 is moved upward (in the z direction) and then laterally (in the x direction) until it is positioned away from the corner plate 1089 of the support arm 82a. The hook 1091 is then retracted (moved in the negative z direction).

[0238] 17H, in a final step the pins 1090 are retracted. Referring to Figure 6, when the pins 1090 are retracted the pellicle frame 17 is no longer supported by the pins 1090 but is supported by its connection with the protrusions 51 protruding from the patterning device MA. In other words, the pellicle frame 17 is attached to and supported by the patterning device MA.

[0239] [000238] The engagement features 50 are secured to the protrusions 51, thereby providing a rigid submount 10 for the pellicle frame (see Figure 3). The pellicle frame 17 is thus securely attached to the patterning device MA. The pellicle, pellicle frame and patterning device (collectively referred to as the mask assembly) can then be placed in a transfer device 853 for transfer to the lithographic apparatus LA (see Figure 2).

[0240] [000239] To remove the engagement features 50 from the projections 51, and thereby remove the pellicle frame 17 from the patterning device MA, the steps shown in Figures 17A to 17H are reversed.

[0241] The step of securing the engagement mechanism 50 to the projection 51 does not require sliding movement between components. In other words, it does not require surfaces to rub against one another in a sliding motion. This is advantageous because such rubbing can be prone to undesirable particle contamination. The step shown in FIG. 17D requires mechanical contact between separate components. Therefore, this step can be particularly prone to particle contamination. The generally convex curved surface provided on the actuation pin 1092 reduces the contact surface area between the actuation pin 1092 and the block 54 compared to an actuation pin without such a curved surface. The generally convex curved surface provided on the actuation pin 1092 also minimizes the risk of sliding (i.e., rubbing) between the surface of the actuation pin 1092 and the surface of the block 54. This avoids the generation of particulate matter that could lead to particle contamination.

[0242] An alternative sequence of steps (not shown) can also be used to attach the engagement features 50 to the protrusions 51. In this alternative sequence, the hooks 1091 are moved into position above the engagement tabs 1089 before the pins are used to raise the pellicle frame 17. Once the hooks 1091 are in position, the pins 1090 are moved upward to compress the engagement features 50. In this manner, the engagement features 50 are gripped by the hooks 1091 and pins 1090. The engagement features 50 are then lifted by moving the hooks 1091 and pins 1090 upward. The same action is performed on the other engagement features 50, thereby lifting the pellicle frame 16. The actuators 111 and imaging sensors 105, 106 (see FIG. 6) are then used to align the pellicle assembly 16 with respect to the patterning device MA. The remaining steps may be as described above with reference to FIGS. 17A-17H.

[0243] 17G, a safety system is provided in connection with the step of engaging the engagement mechanism 50 with the protrusion 51. The hooked member 1091 may not be able to fully disengage from the engagement mechanism 50 before retracting it. For example, if the hooked member 1091 is not moved a sufficient distance in the x-direction as described above, the hooked portion of the hooked member 1091 may overlap with the corner plate 1089 of the support arm 82a. Retracting the hooked member 1091 when it is not fully disengaged from the engagement mechanism 50 may cause damage and / or failure of the pellicle assembly 16 and / or other components. The actuator 111, which controls the z-position of the support structure 101 (which in turn controls the z-position of the hooked member 1091), is operable to be detached from the support structure 101. The actuator 111 is operable to detach from the support structure 101 when the support structure 101 (in response to an actuation force applied to the support structure 101 by the actuator 111) applies a resistance force to the actuator 111 that is greater than a threshold resistance force. This can be described as allowing the support structure 101 to detach from the actuator 111 when movement of the support structure 101 is impeded. Advantageously, the detachable nature of the actuator 111 prevents excessive force from being applied to the engagement mechanism 50. This is beneficial because it prevents damage and / or failure of the pellicle assembly 16 and / or other components if the hooked members 1091 are not fully disengaged from the engagement mechanism 50 before retracting the hooked members 1091.

[0244] [000243] As a modification of the safety system described above, an insert arranged on the upper surface of the support structure 101 can be provided with a hook-like member 1091. The insert can be a removable insert. Rather than the support structure 101 being removable from the actuator 111 when the movement of the support structure 101 is obstructed, the insert can be removed from the support structure 101 when the movement of the support structure 101 is obstructed. The advantages of the safety system described above can also be applied to this modification of the safety system.

[0245] [000244] The features of the two above-described variations of the safety system can be used separately. The features of the two above-described variations of the safety system can be used in combination with each other. Furthermore, variations of the above-described safety system can be provided that achieve substantially the same safety features.

[0246] [000245] An embodiment of a stud fastening device will now be described with reference to Figures 18 to 20.

[0247] [000246] Figure 18 shows a cross-sectional schematic of a stud mounting apparatus 840 according to one embodiment of the present invention. The stud mounting apparatus 840 has similarities to the pellicle frame mounting apparatus 857 shown in Figure 6. Portions of the stud mounting apparatus 840 may correspond to portions of these other devices.

[0248] 10 and 11. The windows 107, 108 are provided in the support structure 101, and imaging sensors 105, 106 (e.g., cameras) are positioned to view the patterning device MA through the windows 107, 108. The imaging sensors 105, 106 shown in FIG. 18 may correspond to the imaging sensors 105, 106 shown in FIGS. 10 and 11. The windows 107, 108 are provided with alignment marks 109 that can be used to align the support structure 101 with respect to the patterning device MA. An actuator 111 is provided to move the support structure 101, and thus the studs 51 held by the support structure 101. The actuators 111 are capable of moving the support structure in the x, y, and z directions, and of rotating the support structure about the z direction. The actuators 111 may be automatic, manual, or semi-automatic (i.e. partly automatic and partly manual). The stud mounting apparatus 840 further comprises an additional support structure 97 configured to support the patterning device MA. This additional support structure may be fixed and is referred to herein as a fixed support structure 97.

[0249] [000248] The base of each stud 51 can be prepared with a preparation liquid. The preparation liquid may be isopropanol (or another alcohol), acetone, or ultrapure water. The preparation liquid may be a mixture of one of these substances with demineralized water. The preparation liquid can be applied to the base of each stud 51 using a swab (such as a microswab). After the studs are created and cleaned, a foil (such as a plastic foil) can be applied to the base of each stud 51. The application of the foil can be performed instead of or in addition to preparing the base of each stud 51 with the preparation liquid. Preparing the studs 51 with the preparation liquid can remove contaminants from the base of the studs 51. Applying the foil to the studs 51 can prevent new contaminants from being deposited on the base of the studs 51. The foil may be removed if the studs 51 are to be attached to a patterning device MA (e.g., immediately before attaching the studs 55 to the patterning device MA).

[0250] [000249] Glue can then be applied to the base of each stud 51 while the stud is held by a stud handling portion 1100 that forms part of the support structure 101. The glue can be applied by a glue dispenser. The glue dispenser can form part of the stud installation apparatus 840. It will be appreciated that the glue can be applied in any known manner. The amount of glue dispensed can be controlled by selecting the glue dispensing pressure and pulse time. The amount of glue dispensed can be controlled using volumetric dispensing. Volumetric dispensing can be beneficial for precise control of the glue when the viscosity of the glue can vary during dispensing.

[0251] [000250] The patterning device MA is then placed on fixed support structure 97 so that it is positioned a few millimeters above support structure 101. Actuators 111 are used to move support structure 101 until alignment marks 109 on windows 107, 108 are aligned with alignment marks on the patterning device MA. Studs 51 are held by stud handling parts 1100 and have fixed positions in the x and y directions relative to support structure 101. The separation distance between studs 51 (there may actually be four) is a fixed, predetermined separation distance. This separation distance between studs 51 matches the separation distance between engagement members 50A-50D provided on pellicle frame 17 (see Figure 3), which will later be attached to the patterning device MA.

[0252] [000251] Once the support structure 101 is correctly positioned relative to the patterning device MA, the support structure 101 is moved upward, closer to the patterning device MA. The stud handling mechanism 1100 is then used to move the studs 51 upward from a position where the bases of the studs 51 do not contact the patterning device MA to a position where they are pressed against the patterning device MA. A heater can then be used to heat the studs 51 to promote curing of the glue at the interface between the bases of the studs 51 and the patterning device MA.

[0253] [000252] A coating of PEEK or some other robust material may be provided at the point where the patterning device MA contacts the stud mounting arrangement 840. Similarly, a coating of PEEK or some other robust material may be provided at the point where the patterning device MA contacts the housing 879.

[0254] 19 shows a portion of the stud attachment apparatus 840 in more detail. The stud handling portion 1100 is shown along with the stud 51 and the patterning device MA (e.g., a mask). Also shown is a partition 842 that separates the environment in which the patterning device is provided from the environment in which the stud handling portion 1100 is provided. The stud handling portion 1100 includes a cup 1102 sized to receive the stud 51 (which may also be referred to as a protrusion), with the underside (i.e., base) of the stud 51 facing outward from the cup 1102. The stud 51 may be held in place within the cup 1102 by gravity. Alternatively, a vacuum mechanism (not shown in FIG. 21 ) may be used to hold the stud 51 in place within the cup 1102. The vacuum mechanism can securely and temporarily hold the stud 51 within the cup 1102. The cup 1102 may be formed, for example, from PEEK or some other robust material. The cup 1102 is held in a handle head 1104, which is supported on a handle body 1106. A spring 1108 is received in contact with a flange 1109 on the handle body, biasing the handle head 1104 and the stud 51 upward. Alignment of the stud 51 with respect to the mask is achieved using the imaging sensors 105, 106 and actuator 111 shown in FIG. 18. Once the actuator has aligned the stud 51 with respect to the patterning device MA, the stud handle 1100 is moved upward to press the stud 51 against the patterning device MA. The stud handles 1100 are moved upward by an actuator (not shown) that moves all four stud handles 1100 simultaneously. When the stud handle 1100 presses the stud 51 against the patterning device MA, the spring 1108 compresses. The springs 1108 partly determine the force that presses the studs 51 against the patterning device MA: a weaker spring will reduce the force that presses the studs against the patterning device, whereas a stronger spring will increase the force that presses the studs against the patterning device.Thus, the force with which the studs 51 are pressed against the patterning device MA can be selected (at least in part) by selecting a spring 1108 with a desired strength. The spring 1108 can, for example, apply an upward pressure to the stud operating portion 1100 and the studs 51. The applied pressure can be, for example, less than 5N.

[0255] [000254] The stud handling portion 1100 can press the studs 51 against the patterning device MA, thereby securing the studs 51 to the mask. As mentioned above, the studs 51 can be provided with a glue or adhesive at their base, and the stud handling portion 1100 can press the studs 51 against the patterning device MA until the glue or adhesive has hardened. Once this has been achieved, the stud handling portion 1100 can be moved away from the patterning device MA (and / or the patterning device MA can be moved away from the stud handling portion 1100).

[0256] In one embodiment, the stud handling portion 1100 may include a heater 1111 configured to heat the studs 51. The heater 1111 may be in the form of an electric heater (e.g., a resistive electric heater). The heater 1111 is used to heat the studs 51 as they are pressed against the patterning device MA. The localized heating of the studs 51 by the heater 1111 is advantageous because it accelerates the curing of the glue or adhesive. This increases the throughput of the stud attachment apparatus 840. The curing performed by heating the studs 51 may be pre-curing or full curing. If pre-curing is used, the patterning device MA and studs 51 may be transferred to an oven for curing. If heating the studs 51 performs full curing, there is no need to transfer the patterning device MA and studs 51 to an oven. This is advantageous because ovens can be a source of contaminating particles.

[0257] [000256] In one embodiment, the stud operating portion 1100 may include an actuator (not shown) operable to press the stud 51 against the patterning device MA (in addition to or instead of the spring 1108). The actuator may also move the cup 1102 away from the stud 51 after the stud has been secured to the patterning device MA.

[0258] [000257] A seal 1112 extends around the periphery of the operator head 1104. The seal 1112 is annular. However, the seal may have any suitable shape. The seal 1112 is formed from a resilient material (e.g., PEEK) and protrudes above the partition 842 and above the studs 51. As a result, when the studs 51 press against the patterning device MA, the seal 1112 is forced downwards. The resilient nature of the seal 1112 means that it forms a seal against the patterning device MA by pressing against it. This encloses the portion of the patterning device MA within the periphery of the seal 1112 and isolates this portion from the portion of the patterning device MA outside the periphery of the seal 1112.

[0259] [000258] Gas extraction channels 1114 are provided in the operator head 1104, extending away from the outer surface of the operator head 1104. An additional gas extraction route is provided by an annular space 1115 around the operator head 1104. Gas delivery channels 1118 are provided on one side of the seal 1112, allowing gas delivery to the area of ​​the patterning device MA positioned within the seal 1112. This is shown schematically by the arrows in Figure 19. Gas is extracted via the gas extraction channels 1114 in the operator head 1104 and the annular space 1115 around the operator head 1104. The gas extraction channels 1114 are distributed around the periphery of the operator head 1104. A gas flow is provided that transports contaminants out of the gas extraction channels 1114 and the annular space 1115, thereby preventing them from adhering to the surface of the patterning device MA. The contaminants may be, for example, particles from glue applied to the studs 51, or chemical vapours from the glue. Chemical vapours may be generated in particular when the glue is heated to harden it. As explained elsewhere, particles or other contaminants on the patterning device MA can cause errors in the pattern projected onto the substrate by the lithographic apparatus, so it is advantageous to use a gas glow to remove the contaminants. The gas may be, for example, air.

[0260] [000259] FIG. 20 illustrates an alternative embodiment of a stud attachment device 843. The stud attachment device 843 illustrated in FIG. 20 shares many features with the stud attachment device 840 illustrated in FIG. 19. The shared features have common reference numbers. For clarity, only a subset of the components of the stud attachment device 843 are shown in FIG. 20. It will be appreciated that the stud attachment device 843 may include any of the above-described features of the stud attachment device 840 illustrated in FIG. 19, as appropriate. The stud attachment device 843 includes an alternative spring mechanism to the spring 1108 of FIG. 19. The stud attachment device 843 includes two leaf springs 1110. The two leaf springs 1110 connect the operating portion body 1106 to the support structure 101.

[0261] [000260] In use, the two leaf springs 1110 provide a generally fixed, defined position for the stud operator head 1100 (and subsequently for the stud 51) in the xy plane. The two leaf springs 1110 allow some relative movement (in the z direction) between the stud operator body 1100 and the support structure 101 (e.g., when the base of the stud 51 contacts the patterning device MA). Thus, when the stud attachment arrangement 843 is pressed down in z, the connection between the operator head 1104 (via the kinematic mount 1130) and the part 1116 (see Figure 19) is lost.

[0262] Advantageously, each leaf spring 1110 is dimensioned to allow movement of the stud operating portion 1100 (relative to the support structure 101) in the z direction but negligible movement in other directions. Furthermore, by using multiple leaf springs 1110 (e.g., two) rather than a single leaf spring, rotation of the stud operating portion 1100 (and consequently the stud 51) in the xz plane, Rxz, is negligible. The arrangement of the leaf springs 1110 in the stud mounting arrangement 843 shown in FIG. 20 ensures that rotation of the stud operating portion 1100 (and consequently the stud 51) about all three axes, as well as translation in the xy plane, is negligible. Thus, the multiple leaf springs 1110 of the stud mounting arrangement 843 offer an advantage over the springs 1108 of the stud mounting arrangement 840 in accurately positioning the stud 51 relative to the patterning device MA.

[0263] [000262] In this document, references to a mask may be construed as a reference to a patterning device (a mask is an example of a patterning device), and these terms may be used interchangeably.

[0264] [000263] In this document, references to glue may be construed as references to adhesives, and these terms may be used interchangeably.

[0265] [000264] Reference has been made to glue in the context of pellicle mounting apparatus (such as pellicle mounting apparatus 855). In particular, glue may be used to attach frame 17 to pellicle 19, and may additionally or alternatively be used to attach engagement features 50A-50D (specifically, ramps 49A-49D) to frame 17. Reference has also been made to glue in the context of stud mounting apparatus (such as stud mounting apparatus 840, 843). In particular, glue may be used to attach studs 51 to patterning device MA.

[0266] [000265] In the environment within an EUV lithography apparatus (which may be under vacuum conditions and may have EUV radiation and / or hydrogen plasma present therein), many known types of glues may have a tendency to outgas. Therefore, in constructing a pellicle assembly and / or a mask assembly, it may be desirable to select a glue that does not outgas (or that does not outgas significantly under such conditions). In practice, this may limit the selection of glues suitable for attaching frame 17 to pellicle 19 or studs 51 to patterning device MA. It is known to use epoxy glue in pellicle mounting systems (to attach frame 17 to pellicle 19) and stud mounting systems (to attach studs 51 to patterning device MA). However, there are drawbacks to using epoxy glue for the above-mentioned purposes.

[0267] [000266] In accordance with one embodiment of the present invention, it is proposed to use a poly(methyl methacrylate) based glue, also known as PMMA glue, in particular in the pellicle mounting apparatus (for attaching frame 17 to pellicle 19 and / or for attaching engagement features 50A-50D to frame 17) and in the stud mounting apparatus (for attaching studs 51 to patterning device MA and / or for attaching frame 17 of pellicle assembly 16 directly to patterning device MA).

[0268] [000267] Such PMMA glues generally include two components that initiate the curing process of the PMMA glue upon contact with one another. These two components can be described as an accelerator and an initiator. Each of the accelerator and initiator may be provided in a resin. Alternatively, the accelerator and / or initiator may be provided in a non-resin material. The viscosity of the accelerator-containing material may be higher or lower than that of the initiator-containing material. It will be appreciated that, as used herein, "resin" refers to any material in which the components of the PMMA glue are provided. Figures 21A and 21B schematically illustrate two example processes for attaching two surfaces to one another using PMMA glue.

[0269] [000268] In Fig. 21A, a surface of a first object B1 is provided with a resin containing an accelerator RA, and a surface of a second object B2 is provided with a resin containing an initiator RI. This is shown in the upper half of Fig. 21A. The surface of a second object B2 is then moved relative to the surface of the first object B1 (as indicated by the arrows) to bring the resin containing the initiator RI into contact with the resin containing the accelerator RA. The resulting mechanism is shown in the lower half of Fig. 21A. The contact between the initiator and the accelerator initiates the curing process of the PMMA glue, thereby bonding the surface of the first object B1 to the surface of the second object B2 by the cured PMMA glue G'.

[0270] [000269] In FIG. 21B, the surface of a first object B1 is provided with multiple rows of resin containing an accelerator RI and multiple rows of resin containing an initiator RI. These rows are arranged so that the rows of accelerator RA and the rows of initiator RI alternate. This is shown in the upper half of FIG. 21A. Next, the surface of a second object B2 is moved relative to the surface of the first object B1 (as indicated by the arrows), compressing the rows of resin on the surface of the first object B1 with the surface of the second object B2. The resulting mechanism is shown in the lower half of FIG. 21B. This compression of the rows of resin RA and RI brings the initiator and accelerator into contact, thereby mixing them and initiating the curing process of the PMMA glue, bonding the surface of the first object B1 to the surface of the second object B2 with the cured PMMA glue G'.

[0271] [000270] It will be appreciated that when the surfaces of the first object B1 and the second object B2 are brought into contact with each other as described above, the surface of the first object B1 may be moved while the surface of the second object B2 is held stationary, or the surface of the first object B1 may be held stationary while the surface of the second object B2 is moved, or both surfaces may be moved.

[0272] [000271] The surface of the first object B1 may correspond to the surface of the pellicle frame 17, and the surface of the second object B2 may correspond to the surface of the pellicle 19. Alternatively, the surface of the first object B1 may correspond to the surface of the pellicle frame 17, and the surface of the second object B2 may correspond to the surfaces of the engagement features 50A-50D. Alternatively, the surface of the first object B1 may correspond to the surface of the stud 51 (e.g., the base surface of the stud 51), and the surface of the second object B2 may correspond to the surface of the patterning device MA. The attachment of the first surface to the second surface may be performed using PMMA glue, as shown in Figure 21A, Figure 21B, or any variant thereof.

[0273] [000272] The curing process of PMMA glue takes several minutes to complete. This is a significantly shorter curing process than the several hours typically required for known epoxy adhesives used in known pellicle mounting systems and known stud mounting systems. Therefore, using PMMA glue to attach pellicle frame 17 to pellicle 19 in accordance with one embodiment of the present invention advantageously significantly reduces the time required to produce pellicle assembly 16 (compared to using known epoxy glues). Similarly, using PMMA glue to attach engagement features 50A-50D to frame 17 significantly reduces the time required to produce pellicle assembly 16 (compared to using known epoxy glues). Additionally, using PMMA glue to attach studs 51 to patterning device MA advantageously significantly reduces the time required (compared to using known epoxy glues). Relatedly, this provides advantages for mass production.

[0274] [000273] PMMA pastes are generally provided as a resin containing an initiator (RI) and a resin containing an accelerator (RA), so PMMA pastes can be described as provided as two or more components.

[0275] [000274] It will be appreciated that all references in this document to glue, particularly references to glue used in pellicle mounting devices (such as pellicle mounting device 855) and stud mounting devices (such as stud mounting devices 840, 843), may be construed as referring to PMMA glue. Furthermore, it will be appreciated that all references in this document to surfaces that are attached or bonded to one another using glue may be construed as referring to surfaces that are attached or bonded to one another using the method shown in Figures 21A and 21B (although this is not limiting and other methods may be used).

[0276] [000275] It may be desirable to remove the glue from a surface. For example, it may be desirable to remove the studs 51 and glue from the patterning device MA. Generally, PMMA glue is more elastic than epoxy glue. PMMA glue can be more easily removed from a surface (e.g., from the surface of the patterning device MA) than epoxy glue. Advantageously, therefore, using PMMA glue to attach the studs 51 to the patterning device MA facilitates stud removal procedures (compared to using known epoxy glues) and patterning device cleaning procedures after the studs 51 have been removed.

[0277] [000275] The pellicle mounting device (such as pellicle mounting device 855) and / or the stud mounting device (such as stud mounting devices 840, 843) may include a heater. The heater may be used to heat the known epoxy glue to accelerate its curing. The component provided with the known epoxy glue may be placed in an oven, and the known epoxy glue may be heated to accelerate its curing. Advantageously, heating is not required to accelerate the curing of the PMMA glue. As a result, the manufacturing procedure may be further simplified, and the risk of defects and damage to the manufactured product (such as pellicle assembly 16 or patterning device MA provided with studs 51) may also be reduced.

[0278] [000277] PMMA glue can be used to form an alternative design of mask assembly 15'. This alternative design of mask assembly 15' offers several advantages over mask assembly 15. This alternative design of mask assembly is described below with reference to Figure 22B and compared to mask assembly 15 shown in Figure 22A.

[0279] [000278] Figure 22A shows a portion of a mask assembly 15 assembled using the apparatus and method described above with reference to Figure 2. Studs 51 are affixed to the patterning device MA using a known epoxy glue G (only one stud 51 is shown in Figure 22A). It may be necessary to apply the known epoxy glue G in a layer having a height (z-direction) of approximately 50 μm. The pellicle assembly 16 includes a pellicle 19 affixed to a pellicle frame 17. Engagement features 50 protrude from the pellicle frame 17 (only one engagement feature 50 is shown in Figure 22A). Each engagement feature 50 engages with a corresponding stud 51, thereby forming the mask assembly 15.

[0280] [000279] Figure 22B shows part of an alternative design of mask assembly 15'. Pellicle assembly 16' includes a pellicle 19 affixed to a pellicle frame 17. Pellicle frame 17 is affixed directly to the patterning device MA using PMMA glue G', which may be provided around the entire periphery of pellicle frame 17. Pellicle assembly 16' is thereby affixed to the patterning device MA, thereby forming mask assembly 15'.

[0281] [000280] Any glue can deform spatially upon curing. PMMA glue G' is relatively elastic (compared to epoxy glue G). Furthermore, the layer onto which PMMA glue G' is applied can be thinner (smaller in the x-direction) and taller (larger in the z-direction) than the layer onto which epoxy glue G is applied. Due to the elasticity of PMMA glue G' and the dimensions to which it can be applied, the deformation of the patterning device MA due to the curing of PMMA glue G' is small. In contrast, if a known epoxy glue G is used to attach a pellicle frame 17 directly to the patterning device MA (as shown in FIG. 22B), the deformation of the patterning device MA due to the curing of the epoxy glue is larger, thereby causing errors in the pattern projected onto a substrate by a lithography apparatus. Therefore, the use of PMMA glue G' can produce a mask assembly 15' that overcomes the problems associated with the use of known epoxy glues G.

[0282] [000281] The mask assembly 15' made possible by the use of PMMA glue G' is advantageous for several reasons as described below.

[0283] [000282] The mask assembly 15' may provide a sealed space (see FIG. 22B) between the pellicle assembly 16' and the patterning device MA. This mask assembly 15' may therefore be described as a "closed frame" system. Advantageously, this may prevent contaminant particles from landing on the side of the patterning device MA facing the pellicle 19, from landing on the side of the pellicle 19 facing the patterning device MA, and / or from entering the space between the pellicle 19 and the patterning device MA. This may prevent such particles from causing errors in the pattern applied to a substrate by the lithographic apparatus.

[0284] [000283] Mask assembly 15' (Fig. 22B) includes fewer components than mask assembly 15 (Fig. 22A). Specifically, mask assembly 15 includes engagement features 50 and studs 51 protruding from pellicle frame 17. Such engagement features 50 and studs 51 are not required in mask assembly 15'. Advantageously, this simplifies the manufacturing process for mask assembly 15' (compared to mask assembly 15). Furthermore, the reduced number of required components and the simplified manufacturing process reduce the manufacturing costs of mask assembly 15' (compared to mask assembly 15).

[0285] 22A, epoxy glue G is provided on the patterning device MA directly below each stud 51. Referring to FIG. 22B, PMMA glue G' is provided on the patterning device MA and between it and pellicle frame 17 so as to contact the pellicle frame 17 around the entire periphery. Therefore, the area of ​​the patterning device MA affixed to pellicle frame 17 in mask assembly 15' (FIG. 22B) is generally much larger than the total area of ​​the patterning device MA affixed to all of the studs 51 in mask assembly 15 (FIG. 22A). That is, the bonding area of ​​the patterning device MA in mask assembly 15' (FIG. 22B) is larger than the bonding area of ​​the patterning device MA in mask assembly 15 (FIG. 22A). The surface of the patterning device MA where the epoxy glue G is provided (FIG. 22A) can be selectively etched to improve adhesion between the epoxy glue G and the patterning device MA. However, such an etched surface is not necessary in mask assembly 15' (Figure 22B) because the bonding area of ​​the patterning device MA in mask assembly 15' is much larger than in mask assembly 15 (Figure 22A). Advantageously, this can reduce the manufacturing time and cost of mask assembly 15' (compared to mask assembly 15).

[0286] [000285] Pellicles may have a shorter lifespan than patterning devices. It may be desirable to replace a pellicle assembly that forms part of a mask assembly. As noted above, PMMA glue is more easily removable than known epoxy glues and is relatively resilient. Advantageously, this allows for easier replacement of a pellicle assembly (such as pellicle assembly 16') that forms part of mask assembly 15'.

[0287] [000286] Although specific reference is made herein to embodiments of the invention in relation to lithography apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus are sometimes referred to generically as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0288] [000287] The term "EUV radiation" is intended to encompass electromagnetic radiation having a wavelength in the range of 4 to 20 nm, for example, in the range of 13 to 14 nm. EUV radiation may have a wavelength of less than 10 nm, such as in the range of 4 to 10 nm, for example, 6.7 nm or 6.8 nm.

[0289] [000288] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein have other applications, such as in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0290] [000289] While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the following claims.

Claims

1. A measurement system for measuring the position of a pellicle assembly, comprising: a radiation source for producing an unpolarized radiation beam; A beam splitter; a quarter-wave plate; an imaging sensor; the radiation source is positioned such that a portion of the unpolarized radiation beam propagates through the beam splitter and the quarter wave plate; the imaging sensor is positioned such that the reflected portion of the unpolarized radiation beam is incident directly on the imaging sensor after passing through the quarter wave plate and the beam splitter.

2. 1. A measurement system for measuring the position of an object relative to a reference object, the object being provided with an object marker, the reference object being provided with a window having a reference marker, the measurement system comprising: a radiation source for generating a beam of radiation; an imaging sensor; the reference marker and the object marker form a reflective diffraction grating; A measurement system wherein the radiation source is positioned such that the radiation beam is incident on the reference marker and the object marker at an angle such that first order diffracted beams of the radiation beam are normally incident on the same imaging sensor.

3. A pellicle frame mounting device comprising the measurement system of claim 1 or 2.

4. a support structure configured to support the pellicle assembly; a linearly movable operating pin configured to move relative to the support structure when supported by the support structure so as to contact a distal end of an engagement arm of an engagement mechanism affixed to a frame of the pellicle assembly and elastically bend the engagement arm; the operating pin extends in a direction substantially perpendicular to the engagement arm and is movable in this direction; the surface of the operating pin is a convex curved surface that minimizes the contact surface area between the surface and the engagement arm; Pellicle frame mounting device.

5. an actuator operable to move the position of the support structure; a plurality of hooked pins disposed on and projecting from the support structure; the plurality of hooked pins are configured to releasably clamp the engagement mechanism in place relative to the support structure during engagement or disengagement of the pellicle assembly and a patterning device; The pellicle frame mounting apparatus of claim 4 , wherein the actuator is removable from the support structure if movement of the support structure is impeded.

6. a support structure configured to hold a patterning device; a stud handling portion configured to contact a stud with the patterning device; the stud operating portion is attached to the support structure using a plurality of leaf springs; Stud mounting device.

7. 7. The stud setting device of claim 6, wherein the stud operating portion comprises a stud holder arranged to hold the stud under gravity or using a vacuum mechanism.

8. Further comprising a glue dispenser, the glue dispenser is configured to provide one or more components of a poly(methyl methacrylate)-based adhesive to a surface of the stud, a surface of the patterning device, or to a surface of the stud and a surface of the patterning device; 8. The stud mounting device of claim 6, wherein when the stud is brought into contact with the patterning device by the stud operating portion, the stud is attached to the patterning device by the poly(methyl methacrylate)-based adhesive.

9. 1. A pellicle mounting apparatus for fabricating at least a portion of a pellicle assembly from a first article and a second article, comprising: a pellicle manipulation unit configured to contact the first article with the second article; a glue dispenser configured to dispense one or more components of a poly(methyl methacrylate)-based adhesive onto a surface of the first article, a surface of the second article, or a surface of the first article and a surface of the second article, such that when the first article is contacted with the second article, the first article is adhered to the second article by the poly(methyl methacrylate)-based adhesive; and A pellicle mounting device comprising:

10. 10. The pellicle mounting apparatus of claim 9, wherein the first article is a frame constructed to provide an enclosed space when the pellicle assembly is bonded to a patterning device.

11. A pellicle and a frame; a poly(methyl methacrylate) based adhesive disposed between and in contact with the pellicle and the frame to affix the pellicle to the frame; Pellicle assembly.

12. 1. A patterning device comprising a plurality of studs, A patterning device, wherein a poly(methyl methacrylate) based adhesive is disposed between the patterning device and each stud of the plurality of studs and is in contact with the patterning device and each stud of the plurality of studs so as to attach the patterning device to each stud of the plurality of studs.

13. 12. The pellicle assembly of claim 11; A patterning device according to claim 12; A mask assembly comprising:

14. a pellicle assembly; a patterning device; the pellicle assembly includes a pellicle and a frame; an adhesive disposed between the frame and the patterning device and in contact with the frame and the patterning device so as to affix the frame to the patterning device; The adhesive is a poly(methyl methacrylate) based adhesive. Mask assembly.

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